Intelligent Items as PCs

This is very much a Work In Progress design document

A group I'm playing with is trying something different: an evil thematic party. I decided to be a sentient item. But I couldn't find anything that fit what I wanted out of it. So I'm creating it!
What's the fantasy / what is this "race" trying to attempt to imitate?
You are essentially a sentient weapon. Meaning:

You have inherent powers

You help (or hinder) the person using you

None of the supplements I found did this. Some made you completely independent of other people, not allowing you to give them anything (but still had to be attuned with them somehow in some cases). In the other extreme, you are an item, and cannot do anything, and your abilities just go to another player (though you can try to assert control).
I want to be able to improve my friend's character. I want to be somewhat dependent on her, but not completely bound and unable to act without her. And I don't think this has to break the math. If she makes double the attacks because she is wielding me, but half are really my attacks, does it break the math?
My alternatives to achieving this otherwise are:

Be a paladin, my auras essentially giving her power like a standard sentient item would

Be a hexblade warlock, my magic weapon powers and few spells I get boosting her

Examples of Items for Inspiration

Sample D&D Sentient Items

Blackrazor

Weapon (greatsword), legendary (requires attunement by a creature of non-lawful alignment)
Hidden in the dungeon of White Plume Mountain, Blackrazor shines like a piece of night sky filled with stars. Its black scabbard is decorated with pieces of cut obsidian.
You gain a +3 bonus to attack and damage rolls made with this magic weapon. It has the following additional properties.
Devour Soul. Whenever you use it to reduce a creature to 0 hit points, the sword slays the creature and devours its soul, unless it is a construct or an undead. A creature whose soul has been devoured by Blackrazor can be restored to life only by a Wish spell.
When it devours a soul, Blackrazor grants you temporary hit points equal to the slain creature's hit point maximum. These hit points fade after 24 hours. As long as these temporary hit points last and you keep Blackrazor in hand, you have advantage on attack rolls, saving throws, and ability checks.
If you hit an undead with this weapon, you take 1d10 necrotic damage and the target regains 1d10 hit points. If this necrotic damage reduces you to 0 hit points, Blackrazor devours your soul.
Soul Hunter. While you hold the weapon. you are aware of the presence of Tiny or larger creatures within 60 feet of you that aren't constructs or undead. You also can't be charmed or frightened.
Blackrazor can cast the Haste spell on you once per day. It decides when to cast the spell and maintains concentration on it so that you don't have to.
Sentience. Blackrazor is a sentient chaotic neutral weapon with an Intelligence of 17, a Wisdom of 10, and a Charisma of 19. It has hearing and darkvision out to a range of 120 feet.
The weapon can speak, read, and understand Common, and can communicate with its wielder telepathically. Its voice is deep and echoing. While you are attuned to it, Blackrazor also understands every language you know.
Personality. Blackrazor speaks with an imperious tone, as though accustomed to being obeyed. The sword's purpose is to consume souls. It doesn't care whose souls it eats, including the wielder's. The sword believes that all matter and energy sprang from a void of negative energy and will one day return to it. Blackrazor is meant to hurry that process along.
Despite its nihilism, Blackrazor feels a strange kinship to Wave and Whelm, two other weapons locked away under White Plume Mountain. It wants the three weapons to be united again and wielded together in combat, even though it violently disagrees with Whelm and finds Wave tedious.
Blackrazor's hunger for souls must be regularly fed. If the sword goes three days or more without consuming a soul, a conflict between it and its wielder occurs at the next sunset.

Moonblade

Weapon (longsword), legendary (requires attunement by an elf or half-elf of neutral good alignment)
Of all the magic items created by the elves, one of the most prized and jealously guarded is a moonblade. In ancient times, nearly all elven noble houses claimed one such blade. Over the centuries, some blades have faded from the world, their magic lost as family lines have become extinct. Other blades have vanished with their bearers during great quests. Thus, only a few of these weapons remain.
A moonblade passes down from parent to child. The sword chooses its bearer and remains bonded to that person for life. If the bearer dies, another heir can claim the blade. If no worthy heir exists, the sword lies dormant. It functions like a normal longsword until a worthy soul finds it and lays claim to its power.
A moonblade serves only one master at a time. The attunement process requires a special ritual in the throne room of an elven regent or in a temple dedicated to the elven gods.
A moonblade won't serve anyone it regards as craven, erratic, corrupt, or at odds with preserving and protecting elvenkind. If the blade rejects you, you make ability checks, attack rolls, and saving throws with disadvantage for 24 hours. If the blade accepts you, you become attuned to it and a new rune appears on the blade. You remain attuned to the weapon until you die or the weapon is destroyed.
A moonblade has one rune on its blade for each master it has served (typically 1d6 + 1). The first rune always grants a +1 bonus to attack and damage rolls made with this magic weapon. Each rune beyond the first grants the moonblade an additional property. The DM chooses each property or determines it randomly on the Moonblade Properties table.
Moonblade Properties
d100 Property
01-40 Increase the bonus to attack and damage rolls by 1, to a maximum of +3. Reroll if the moonblade already has a +3 bonus.
41-80 The moonblade gains a randomly determined minor property (see "Special Features" in the Dungeon Master's Guide).
81-82 The moonblade gains the finesse property.
83-84 The moonblade gains the thrown property (range 20/60 feet).
85-86 The moonblade functions as a defender.
87-90 The moonblade scores a critical hit on a roll of 19 or 20.
91-92 When you hit with an attack using the moonblade, the attack an extra 1d6 slashing damage.
93-94 When you hit a creature of a specific type (such as dragon, fiend, or undead) with the moonblade, the target takes an extra 1d6 damage of one of these types: acid, cold, fire, lightning, or thunder.
95-96 You can use a bonus action to cause the moonblade to flash brightly. Each creature that can see you and is within 30 feet of you must succeed on a DC 15 Constitution saving throw or become blinded for 1 minute . A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. This property can't be used again until you take a short rest while attuned to the weapon.
97-98 The moonblade functions as a ring of spell storing.
99 You can use an action to call forth an elfshadow, provided that you don't already have one serving you. The elfshadow appears in an unoccupied space within 120 feet of you. It uses the statistics for a shadow from the Monster Manual, except it is neutral, immune to effects that turn undead, and doesn't create new shadows. You control this creature, deciding how it acts and moves. It remains until it drops to 0 hit points or you dismiss it as an action.
00 The moonblade functions as a vorpal sword.
Sentience. A moonblade is a sentient neutral good weapon with an Intelligence of 12, a Wisdom of 10, and a Charisma of 12. It has hearing and darkvision out to a range of 120 feet.
The weapon communicates by transmitting emotions, sending a tingling sensation through the wielder's hand when it wants to communicate something it has sensed. It can communicate more explicitly, through visions or dreams, when the wielder is either in a trance or asleep.
Personality. Every moonblade seeks the advancement of elvenkind and elven ideals. Courage, loyalty, beauty, music, and life are all part of this purpose.
The weapon is bonded to the family line it is meant to serve. Once it has bonded with an owner who shares its ideals, its loyalty is absolute.
If a moonblade has a flaw, it is overconfidence. Once it has decided on an owner, it believes that only that person should wield it, even if the owner falls short of elven ideals.

Wave

Weapon (trident), legendary (requires attunement by a creature that worships a god of the sea)
Held in the dungeon of White Plume Mountain, this trident is an exquisite weapon engraved with images of waves, shells, and sea creatures. Although you must worship a god of the sea to attune to this weapon, Wave happily accepts new converts.
You gain a +3 bonus to attack and damage rolls made with this magic weapon. If you score a critical hit with it, the target takes extra necrotic damage equal to half its hit point maximum.
The weapon also functions as a Trident of Fish Command and a Weapon of Warning. It can confer the benefit of a Cap of Water Breathing while you hold it, and you can use it as a Cube of Force by choosing the effect, instead of pressing cube sides to select it.
Sentience. Wave is a sentient weapon of neutral alignment, with an Intelligence of 14, a Wisdom of 10, and a Charisma of 18. It has hearing and darkvision out to a range of 120 feet.
The weapon communicates telepathically with its wielder and can speak, read, and understand Aquan. It can also speak with aquatic animals as if using a speak with animals spell, using telepathy to involve its wielder in the conversation.
Personality. When it grows restless, Wave has a habit of humming tunes that vary from sea chanteys to sacred hymns of the sea gods.
Wave zealously desires to convert mortals to the worship of one or more sea gods, or else to consign the faithless to death. Conflict arises if the wielder fails to further the weapon's objectives in the world.
The trident has a nostalgic attachment to the place where it was forged, a desolate island called Thunderforge. A sea god imprisoned a family of storm giants there, and the giants forged Wave in an act of devotion to — or rebellion against — that god.
Wave harbors a secret doubt about its own nature and purpose. For all its devotion to the sea gods, Wave fears that it was intended to bring about a particular sea god's demise. This destiny is something Wave might not be able to avert.

Whelm

Weapon (warhammer), legendary (requires attunement by a dwarf)
Whelm is a powerful warhammer forged by dwarves and lost in the dungeon of White Plume Mountain.
You gain a +3 bonus to attack and damage rolls made with this magic weapon. At dawn the day after you first make an attack roll with Whelm, you develop a fear of being outdoors that persists as long as you remain attuned to the weapon. This causes you to have disadvantage on attack rolls, saving throws, and ability checks while you can see the daytime sky.
Thrown Weapon. Whelm has the thrown property, with a normal range of 20 feet and a long range of 60 feet. When you hit with a ranged weapon attack using it, the target takes an extra 1d8 bludgeoning damage, or an extra 2d8 bludgeoning damage if the target is a giant. Each time you throw the weapon, it flies back to your hand after the attack. If you don't have a hand free, the weapon lands at your feet.
Shock Wave. You can use an action to strike the ground with Whelm and send a shock wave out from the point of impact. Each creature of your choice on the ground within 60 feet of that point must succeed on a DC 15 Constitution saving throw or become stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Once used, this property can't be used again until the next dawn.
Supernatural Awareness. While you are holding the weapon, it alerts you to the location of any secret or concealed doors within 30 feet of you. In addition, you can use an action to cast Detect Evil and Good or Locate Object object from the weapon. Once you cast either spell, you can't cast it from the weapon again until the next dawn.
Sentience. Whelm is a sentient lawful neutral weapon with an Intelligence of 15, a Wisdom of 12, and a Charisma of 15. It has hearing and darkvision out to a range of 120 feet.
The weapon communicates telepathically with its wielder and can speak, read, and understand Dwarvish. Giant, and Goblin. It shouts battle cries in Dwarvish when used in combat.
Personality. Whelm's purpose is to slaughter giants and goblinoids. It also seeks to protect dwarves against all enemies. Conflict arises if the wielder fails to destroy goblins and giants or to protect dwarves.
Whelm has ties to the dwarf clan that created it, variously called the Dankil or the Mightyhammer clan. It longs to be returned to that clan. It would do anything to protect those dwarves from harm.
The hammer also carries a secret shame. Centuries ago, a dwarf named Ctenmiir wielded it valiantly for a time. But Ctenmiir was turned into a vampire. His will was strong enough that he bent Whelm to his evil purposes, even killing members of his own clan.

Docent

Wondrous item, rare (requires attunement by a warforged)
A docent is a small metal sphere, about 2 inches across, studded with dragonshards. To attune to a docent, you must embed the item somewhere on your body, such as your chest or your eye socket.
Sentience. A docent is a sentient item of any alignment with an Intelligence of 16, a Wisdom of 14, and a Charisma of 14. It perceives the world through your senses. It communicates telepathically with you and can speak, read, and understand any language it knows (see "Random Properties" below).
Life Support. Whenever you end your turn with 0 hit points, the docent can make a Wisdom (Medicine) check with a +6 bonus. If this check succeeds, the docent stabilizes you.
Random Properties. A docent has the following properties:
Languages. The docent knows Common, Giant, and 1d4 additional languages chosen by the DM. If a docent knows fewer than six languages, it can learn a new language after it hears or reads the language through your senses.
Skills. The docent has a +7 bonus to one of the following skills (roll a d4): (1) Arcana, (2) History, (3) Investigation, or (4) Nature.
Spells. The docent knows one of the following spells and can cast it at will, requiring no components (roll a d6): (1-2) Detect Evil and Good or (3-6) Detect Magic. The docent decides when to cast the spell.
Personality. A docent is designed to advise and assist the warforged it's attached to. One of the simple functions of a docent is to serve as a translator. The docent's properties are under its control, and if you have a bad relationship with your docent, it might refuse to assist you.

Sample Pathfinder Intelligent Items

Shield of the Mage

Price 14,500 gp; Aura moderate divination; CL 11th; Weight 5 lbs.
Alignment neutral; Senses 30 ft.
Intelligence 16; Wisdom 10; Charisma 10; Ego 6
Language telepathy (Common and six other languages)
This caster's shield always has one arcane scroll and knows the same arcane spells as the wielder. When the spell on the scroll is cast, another scroll of a spell the wielder knows randomly manifests to replace it. The shield has no arcane spell failure. The shield can also read magic. It will often debate with its wielder for the most devastating course of action, but does what the wielder commands.
CONSTRUCTION REQUIREMENTS
Cost 7,250 GP
Craft Magic Arms and Armor, Scribe Scroll, creator must be an arcane spellcaster of at least 14th level

Lightning Bow

Price 54,300 gp; Aura strong evocation; CL 17th; Weight 3 lbs.
Alignment neutral; Senses 120 ft.
Intelligence 6; Wisdom 11; Charisma 11; Ego 9
Language speech (Auran)
This intelligent item is called a lightning bow by mortals, a name is seen as a slight to the lightning elemental trapped within it—a creature honor-bound to serve in the bow for no less than 100 years. Each of these +3 adaptive composite longbows is a haughty and often highly intelligent member of its race, who chides those who don't know its true name—which is often a complicated series of high pitched squeaks, like live wood burning on a pyre. The elemental in a lightning bow only speaks Auran. Lightning bows will not fire on other outsiders with the elemental subtype. Some are also bound not to attack other individuals, based on their history. For instance, one of these bows might be foresworn not to attack the Sultan of Fire, fire giants, or red dragons. Additionally, lightning bows have the following powers.
A lightning bow needs no ammunition. With the pull of a string, it creates a +3 shock arrow or a +3 brilliant energy arrow (the wielder's choice with each shot). Three times per day, the wielder can cast true strike as a swift action. The true strike can only be used with attacks made with the lightning bow. Three times per day, the wielder can use lightning bolt as a spell-like ability.
CONSTRUCTION REQUIREMENTS
Cost 27,300 GP
Craft Magic Arms and Armor, call lightning, the willing service of one Huge lighting elemental for at least 100 years

Hammer of Enemies

Price 54,212 gp; Aura moderate conjuration; CL 10th; Weight 5 lbs.
Alignment chaotic neutral; Senses 30 ft., darkvision
Intelligence 10; Wisdom 16; Charisma 14; Ego 14
Language speech (Common)
This special +3 bane warhammer seeks only to crush the enemy of its wielder in battle. The hammer can speak Common, constantly mutters, curses when it is not engaged in battle, and sings deeply of its love of carnage when it is being used in a fight. The hammer of enemies is always eager to point out potential enemies within its vision. Because of its bloodlust it does not bestow negative levels on creatures that do not share its alignment—it is willing to fight for anyone. Additionally, three times per day, the hammer of enemies can change the creature type of its bane ability. A creature type remains until a new one is chosen.
CONSTRUCTION REQUIREMENTS
Cost 27,262 GP
Craft Magic Arms and Armor; monster summoning IV

Design Ideas

"Race" Abilities

A few inherent abilities to all intelligent items

A few specific ideas to the weapon type

Much of the following race abilities have been copied from constructs.
Ability Scores. A sentient magic item has Intelligence, Wisdom, and Charisma scores. Your Intelligence score increases by 2, and one other ability score of your choice increases by 1.
You use your Wisdom score when making a Strength saving throw, your Intelligence when making a Dexterity saving throw, and your Charisma when making a Constitution saving throw. You cannot make Strength, Dexterity, or Constitution ability checks. When targeted by dispel magic, you must succeed on a Constitution (Charisma) saving throw or become unconscious for 1d6 + 1 rounds. if you roll a 1 on your save, you become a mundane weapon. While you are in an antimagic field, you are incapacitated, blinded, and deafened.
Alignment. You can be any alignment. If you are any alignment that is not TN, you gain the ability to repel creatures of opposite alignment to yours. When such a creature tries to use you, you can....
Speed. You cannot move on your own, unless you obtain magical abilities to do so. Your speed is 0.
Built-in Resilience. As a creature created with a non-living body, you have the following benefits:
You have advantage on saving throws against being poisoned, and you have resistance to poison damage.
You don’t need to eat, drink, or breathe.
You are immune to disease.
You don't need to sleep, and magic can't put you to sleep.
Special Purpose. You were created for a specific reason. When you are acting directly (eg: if your purpose is to banish all elves, you gain this damage when fighting elves, but not when fighting their allies etc) to fulfil your purpose, you gain additional powers:
You deal additional damage in your attacks. 1d6 from levels 1 to 6, 1d8 from levels 7 to 12, and 1d10 from levels 13 and onwards. You gain additional charges or effects of your special powers (if the power doesn't state a level-up ability, you gain an additional charge unless indicated otherwise).
Power Down. Items need no sleep, but their intelligent minds need rest. You need at least 4 hours a day of mental inactivity. During this time you remain semi-conscious. After resting in this way, you gain the same benefit a human would from 8 hours of sleep.

Subrace / Item Abilities

Sentient Item Class / Powering your Sentient Item

Ideally, how you level up is related to your special purpose. If your purpose is to consume souls, you level up after consuming a number of souls. If your purpose is to consume magic items, you level up after consuming a number of magic items, etc. However, this may get too finicky. Talk to your GM about the possibility of making this happen, otherwise, simply use the same method to level the rest of the characters are using.
Below are two examples of levelling following your special purpose.

Eating magic items

Level 1: Consume a consumable magic item (eg: potion or oil)
Level 2: Consume two consumable magic item (eg: potion or oil)
Level 3: Study a common magic item
Level 4: Consume a common magic item
Level 5: Study an uncommon magic item
Level 6: Study an uncommon magic item
Level 7: Consume an uncommon magic item
Level 8: Study a rare magic item
Level 9: Study a rare magic item
Level 10: Study a rare magic item
Level 12: Consume a rare magic item
Level 13: Study a very rare magic item
Level 14: Study a very rare magic item
Level 15: Study a very rare magic item
Level 16: Study a very rare magic item
Level 17: Consume a very rare magic item
Level 18: Study a legendary item
Level 19: Study a legendary item
Level 20: Consume a legendary item

Study: attunement for at least 24 hours or 24 hours (do not have to be consecutive) of study
Consume: absorbing the item's magic, which leaves the item inert and non-magical

Power-up abilities

These abilities could be based on the item being studied or consumed, or based on the following powers:

Example: Sense (rarity): explanation (power increase details if any)

Communication

Empathy (common): you communicate through feelings and emotions with the person holding you (you can affect anyone within 30 ft. of you)

Owner telepathy (common): you can telepathically communicate with the person attuned to you (even while they are not holding you up to 1 mile of distance)

Holder telepathy (uncommon): you can telepathically communicate with the person holding you (while they hold you, you understand every language the holder knows)

Blood telepathy (uncommon): you can telepathically communicate with people who you have tasted their blood in the last 7 days (the length is extended to 28 days)

Oracle (rare): you can communicate your intentions through visions and dreams, while your wielder is unconscious (you can force visions to your wielder while they are awake)

Combat

Magic weapon (common): +1 bonus to attack and damage rolls made with you (increase to +2)

Bane of my enemies (common): you have a grudge against a creature type and can instruct your wielder in the best way to annihilate them, you deal an additional 1d6 damage against that creature (you have two creatures that you have extensive battle experience against)

Magic damage (common): you deal an additional 1d4 elemental damage, choose the damage type [acid, cold, fire, lightning, or thunder] once when choosing this ability (damage increases to 3d4)

Critical prowess (uncommon): attacks with you score a critical hit on a roll of 19 or 20 (your wielder gains the increased critical threat with all of their attacks, as long as they are attuned to you)

Critical siphon (rare): when you score a critical hit, you gain temporary hit points equal to half the damage dealt (you regain normal hit points, any excess that would go over your normal max hp is converted into temporary hp)

Return (rare): when you leave your holder's hands, for example, when thrown, but also when disarmed, your holder can use a bonus action to call you back to their hand (you can return to your holder's hand immediately, without their input; if you wielder doesn't have a hand free, you land at their feet.)

Magic

Arcane knowledge (common): your arcane knowledge grants your wielder a +1 in their Arcane skill (your knowledge gives your wielder a +3)

Magical senses (common): your wielder can use an action to cast Detect Evil and Good once per day (your wielder can also cast Detect Magic; each detect spell uses 1 charge, and you have 3 charges per day, which recharge at dawn)

Spell sniper (uncommon): your wielder gains a +1 to their spell attack bonus (your wielder gains a +3 to their spell attack bonus)

Spell mastery (uncommon): your wielder gains a +1 to their spell DC (your wielder gains a +3 to their spell DC)

Striker (uncommon): once per day, you can cast True Strike to encourage your wielder to strike true to that target (your wielder must use its next attack action to target the creature you cast true strike on)

Spell defender (rare): your wielder gains advantage against spells (your wielder gains resistance against spells)

Spell knowledge (rare): you have arcane knowledge, which allows you to store a spell for your wielder, functioning as a ring of spell storing (you can store spells up to 7th level, rather than up to level 5)

Arcane damage (very rare): your wielder adds their casting ability score modifier to the damage they deal with their spells (your wielder adds double their casting ability score modifier to the damage they deal with spells)

Special Actions

Tremble (uncommon): Your wielder can use an action to strike the ground with you and send a shock wave out from the point of impact. Each creature of within 30 feet of that point must succeed on a DC 15 Constitution saving throw or become stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Once used, this property can't be used again until the next dawn. (the range increases to 60 feet)

Senses

Hidden doors (common): While your wielder holds you, you can alert them to the location of any secret or concealed doors within 15 feet of you (the range increases to 40 feet)

Trapper knowledge (common): While your wielder holds you, you can alert them to the location of any non-magical traps within 15 feet of you (you can detect magical traps)

Hatred (uncommon): if you have "Bane of my enemies", you can detect the presence of those creatures within 120 feet of you (the range extends to 1 mile)

Detect others (uncommon): you can detect other magic items within 30 feet of you (your range extends to 90 feet)

Inspirations / References:

Why you should play Sentient Weapons by Rookzer0

This is kind of the closest to my dream, but too stripped down of independence for the player

The Awakened Item by Spilled Ale Studios

The race and class idea is neat, but "You can’t take the Attack action while you are being worn" destroys the dream

Magic Items as Characters by Owen Parker

Some interesting ideas & magical abilities

Animated Weapon by Ethan Lefevre (Knock #1)

Cool titles, cool dispel magic mechanics