Necrotic Magic

Necromancy is a form of magic that is revered or feared, and seldom anything in between. On one hand, its ability to commune with the deceased and provide spirit counselling services is extremely valuable, while on the other its various foul abilities to upend the natural order make many individuals inherently antsy - and for good reason.

— Shirahime, High Mage of the Kisupet Empire

Necrotic Magic, also known as Necromancy, is a form of magic with a quite... troubled past. Known for many 'good' powers, but many more foul ones, its reputation is spotty, to say the least. Many still don't entirely know how to regard Necromancy's suite of powers, and while some realms ban it entirely, some don't regulate it at all, and many only regulate its most dangerous aspects.

History of Necrotic Magic

Ancient History

Little is known for sure on how much - if at all - the Hysilens made use of or tolerated Necrotic Magic; the records are very clear that they knew of it, but not so clear on if they made active use of it; in many senses, this is a yet-unanswered question which may prove pivotal to the general acceptance of decline of the art, as it's no secret that the societies of the world tend to follow the Hysilens' view on magic for the most part - though not entirely.
That being said, while there are few records of what the Hysilens did with the magic, there are plenty regarding the Raqise and their exploits. The Raqise didn't start dabbling into Necromancy until the later days of the Confederacy, but when they did, they did so in heinous style, exploring its most damning parts; soul sacrifices, the raising of undead, and much more besides. It's even said that the first Tal'ayn Necrarch was a Raqise who experimented on the magic at the capital of the Confederacy.

Early History

The collapse of the Confederacy saw a few important things happen with regards to necrotic magic; a big one was the halting of the heinous experiments, but also the founding of the Tal'ayn vampire coven which specialized in it - and specifically necrarchy - in the following decades. Indeed, the Raqise's role in the founding of the Tal'ayn is so great that it's said that their coven matriarch is the sole remaining Raqise, though that's... difficult to confirm, with the impossibility of finding the coven for outsiders to begin with.
Beyond that, however, necromancy in general began to butt heads with Divine Magic and the agents of the ecclesiarchies such as Clerics and Paladins, paving the way to a famously tense and back-and-forth conflict to begin between the two sides. This era was also precipitated by the first development of free-thinking undead species which only further made things complicated.

Modern History

Nowadays, however, many tens of thousands of years have passed since then, and many realms permit citizens to practice limited necromancy. Some - such as the princedoms of the Ragnarian Mudlands - allow for the practice to be done in the open, but require that the raising of undead only be done for as long as undead are required for combat purposes, requiring their release from undeath afterwards.
Others, like the Kisupet Empire and the Bhailu Empire, maintain those strict bans on the art, albeit with the Imperial Bhailu Army allowing for so-called Sanctioned Necromancers to operate with their blessing. In general, much has changed since the time of the Raqise's embracement of necromancy, and the Necromancers themselves are not nearly as free to act as they were back then. For the most part, however, Necrotic interest in the modern age is focused on the studies of the Hysilens, to hopefully provide validation to their very existence.

Necrotic Shards

Necrotic Shards are a... complicated type of shard, not easily found naturally across the world, they generally follow similar rules to Memoria Shards, incidentally; events with great casualties are typically what spur forth necrotic shards in their myriad forms, to be harvested and used for a myriad purposes.
Unlike most other forms of shard, necrotic shards are vital for far more than just the creation of new Necromancers; their power is directly responsible for permitting powerful undead to be risen, and many exceptionally strong undead - such as Liches and Grave Queens - embed shards as part of their very bodily construction, as the shards serve a dual purpose of indefinitely sustaining their existence while also boosting their powers considerably.
These factors combine to make the shards uncommon in times of peace and plentiful in times of great upheaval, which is perhaps why the Raqise had access to so many, the ebbs and flows following that of the undead themselves very closely. A notable caveat to necrotic shards is that the events that lead to their creation can also lead to Blood Shards or Demonic Shards, all pretty more entirely dependent on other factors such as the entities involved in the death events.

Uses of Necrotic Magic

Necromancer Coven by Bram Willemot

Communions

Communions are one of the first skills a budding Necromancer learns, and it's the one the art is generally most known for in a good light. Communions allow a Necromancer to form a link with a being that has passed on, to allow their family to speak with them one last time and such.
As a form of communication, communions are quite restricted, requiring the being to have passed on recently, while being willing to communicate with the Necromancer and their clients, but beyond that is generally a very passive and safe form of the art, allowing for relatives to make peace with the events, for a Necromancer to aid a troubled spirit with passing on, and much more.
It's no coincidence that many of the Necromancers accepted and embraced by society are these kinds of necromancer, rather than any other.

Life Siphoning

Life Siphoning magic is one of the most common applications of necrotic magic, as it allows the Necromancer to siphon their victim's vitality into themselves. Life Siphoning is a very... contentious form of magic, as it not only allows for a Necromancer to heal themselves, but to also extend their natural lifespan, potentially indefinitely.
Those generally born with an affinity for necrotic magic are very liable to hide it in most societies, but even still will actively use life siphoning in secret on either unsuspecting targets or on their prisoners, which certainly places a stigma on those who look younger than their age and who are not known immortal races such as the kitsune Vulpinari.
Even still, life siphoning isn't outright illegal in most regions of the world, but the pursuit of unnatural immortality through it generally is.

Offensive Necrotic Magic

Hinted at in its name, necrotic magic can also be utilised offensively through the medium of necrosis, dealing damage at range or spreading diseases to targets. It essentially allows a Necromancer to inflict traditional wounds at larger ranges than traditionally possible, while also allowing them to magically worsen those wounds.
Even more, it can be used to both spread and precisely control virulent plagues and diseases, which is a double-edged sword reputationally; it can be used to effortlessly spread brutal diseases and plagues, but can also completely stem and prevent their spread in an instant.

Necromantic Undead

Unsurprisingly, the first thing that generally comes to mind when discussing Necrotic Magic is the undead. This is, naturally, to be expected, as the most notorious Necromancers often control small armies of undead beings. Traditional doctrine teaches that life ends after death, but budding Necromancers attempt to bypass these problems. They don't do it by reviving the dead though, but rather by turning them into mindless undead.
That said, this isn't Necrarchy, and so there exists numerous stringent rules which govern the raising necromantic undead. The most important one, is that it's very short term, heavily taxing a Necromancer's Aspected Aether reserves to maintain a necrotic force. This generally means that a Necromancer has to maintain a small number of undead, and generally opts for quality over quantity. Moreover, the soul of the body they wish to raise has to have already fully passed into the afterlife, as they are not shackling the soul of that body back into it to reanimate it, in spite of common conjecture, they're merely animating the body with their own Aether.
This results in Necromantic Undead being potent and dangerous in the right hands, but generally being quite niche and restrictive... A far cry from the powers of the Tal'ayn vampires and Tal'ayn Necrarchs in general.

Mornhaven Attack by Bram Willemot

Necrarchy

The infamous Tal'ayn Vampires - the eponymous necrotic vampires - are a truly terrifying coven of vampire blessed with all of the wondrous powers and abilities of the vampire race - alongside the Tal'ayn specific covenant powers - along with powerful undead-controlling capabilities as their form of vampiric blessing.
Necrarchy is the culmination of Tal'ayn spellcraft, and effectively acts to look at all of the restrictions of traditional Necromancy, and overturn them. Nobody quite knows how it does this, as the Tal'ayn are infamously reclusive about sharing any information about their abilities except for with powerful free-spirited undead such as Grave Queens - in spite of being a quite sociable Vampire Covenant (at least, when you're not asking where their Matriarch is) - but what is known, is the terrifying breadth of power that Necrarchy possesses.
As a form of magic, Necrarchy possesses all other forms of necrotic magic, but with them being exceptionally Aether-efficient, and thus much more dangerous to face against as the Tal'ayn Necrarchs already have far greater capabilities than normal. Where the magic really starts to get unhinged however, is with Necrarchic Undead. They're much like regular undead, except that the Necrarch can substitute their Aether-drain for a few things, most famously for the power of a Necrotic Shard, generally built into the design of their magical focus.
This simple change derives the power of the shard to sustain an enormous number of undead through techniques nobody really understands, but it clearly has its limits, as for the most powerful raised undead, the Tal'ayn without fail embed a shard into those undead's forms as a portable source of necrotic energy.
The other thing they can substitute the Aether-drain for, however, is far darker; a Tal'ayn Necrarch can draw forth the soul of the deceased from the afterlife and force it back into the body, only heavily shackled to forever follow the will of the Necrarch. These are what are generally known as Soulful Undead; those who have had their very being ripped from the afterlife and reanimated into undeath forever.
The creation of soulful undead isn't unique to Necrarchy - and is generally how most powerful undead come into being, albeit unshackled to any Necromancer or Tal'ayn Necrarch - but Necrarchy can definitely be said to have made its potency well known to all.