Side Story: Alchemist and a Broken One

One day, while looking through the requests on the ReQuest Board characters see the note asking for the help in bringing something from the ruins nearby. If they decide to help, the note will point them to the address of the one, who posted it.
Their destination is an old, two-story house made out of black wood with a pretty big backyard.
After ringing the bell, the door will be opened by Diuna, a homunculus.
She will ask them if they are here because of the request. After the confirmation, she will tell them the master of the house awaits them and will ask them to follow her. Diuna will lead them upstairs to the study (on the way they will pass a few of the rooms with strange instruments in them. Additionally, even the least perceptive of them will notice there are Elemental Crystals hanging everywhere).
The room they'll reach is almost completely dark, with only one light source being the desk lamp. Near the desk, with a back turned to them, sits a man reading something. He'll speak:

"Who was that, Diuna?"
"Viktor, we have guests. They are here because of your request.", she answers.

Immediately, he'll turn around, stand up and shake off the dust of his clothes.

"Welcome. My name is Viktor Wolf and I am a researcher and alchemist. You already know Diuna", he points to her, she makes a little bow.
"She is my assistant, helper, and a dear friend. I wanted to hire you to help me carry out an ancient artifact from the ruins nearby the settlement. It is possible there will be monsters there. I am ready to pay you the third of the promised sum now and the rest after the work."

If characters agree, he will ask them to wait downstairs as he and Diuna need to prepare themselves to go to the ruins (if characters need to buy some things before leaving the settlement, Viktor will propose to meet at the gate in an hour or two).
Diuna will join them a few minutes later. If they ask her about the job, she will tell them to direct their questions to Viktor, as she doesn't really know what he is doing this time.
Another few minutes later Viktor walks down the stairs and the party is finally ready to move out.
The journey will be fairly short and peaceful thanks to the closeness of the settlement (they can, however, encounter a few monsters). If the characters decide to ask Viktor about the request, he will explain that they are going to retrieve a tablet that, as he believes, contains the knowledge about The Guardians of The Tree, which could push his research forward. Their destination is a ruin of an old high school that partially collapsed under the ground. What awaits them next is straightforward - go in, retrieve the tablet, fight off monsters, go out.
After a job is well done and bringing the tablet to Viktor's place, he will pay them, thank them, and when he will end the translation, he can share the knowledge of the tablet with them.
Random Meeting

After the job is done, sometime later, characters meet Diuna doing the shopping at the market. She will ask them to help her carry the bags she has.
The same day, Bard arrived at the settlement and right now he plays songs for the crowd at the same market. When he notices Diuna, he stops playing for a few seconds (only really perceptive characters will notice that).
When characters reach the Viktor's house, Diuna will thank them and tell them that the translation is almost complete.

Second Job

While searching for another job at the Request Board, there will be a new request left by the Viktor. Optionally, characters could just go to him because they were curious if the translation is complete.

"It's incomplete. Well, my translation is complete, but the tablet is not. This was just the first part. However, its author has left the clues about where he has left the second part. I already know where it is. So, I need your help again."

Just like before, he will lead everyone to the ruin of the high school, but this time they will go to the deeper, more dangerous part of it. But this time, while returning, something will happen to Diuna. She will start shaking and as soon as Viktor will see that, he will scream:

"Get to the cover, fast!"

As soon as characters do that, he will run to Diuna, but just before he reaches her, an explosion of Elements will hit him and everything around: flames, lightning, and earthen shards. It lasts only a few seconds and as soon as it ends, Diuna collapses.
Viktor will bandage his hands and will start to carry Diuna back home. If asked about the incident, he will just say:

"It's nothing."

After reaching the house, he will pay the characters, tell them to come back in a week, and dismiss them.

Research

Week later, when characters ring the bell to his door, he will open them instead of Diuna. If asked about that, he will say:

"She rests."

He will lead them to his study. This time there are papers everywhere, all of them covered with his scribbles. In the light, characters can notice that Viktor has more bandages on his body.
He will tell them what he has discovered.
According to his research, some of the seven great Guardians of The Tree could possibly walk among other people. The texts said that one of them, the Mage, was supposed to spread the magic all around The Pit to the point even a child could cast spells and manipulate Elements. Instead, he disappeared.
That was pretty much all that was in the tablets, however, there are hints of the third one. He just needs some time to localize it.

Third job

Again, there will be another request on the Request Board.
This time, when characters ring the bell, it will take some time before someone answers it.
Viktor opens the door. He looks awful as if he cried for the last few days and didn't sleep. He talks very quietly:

"Oh, yeah, I am sorry. I forgot to take the request down from the board. It doesn't matter anymore. The job is canceled. I am sorry you had to come here. Thank you for your help, but could you leave for now?"

Next days

For the next few days, if the characters try to go to the Viktor's house, no one will answer them.
Finally, after a week, the door will be opened by someone characters don't know.

"Hello, are you here to see my brother? I am Markus Wolf. I am afraid you have come here at a very bad time. Some time ago, Viktor has lost someone really dear to him, and right now he isn't really in the right state to talk with anyone. I came here to take him back home, so he can rest. If you are his friends, this is our address (he will give them a note). Please, visit whenever you want, just...give him some time.

Aftermath

Not long after this Viktor's house will be put up for sale.
If the characters ever go to his family's home, they will discover that a week after arriving there, Viktor has disappeared without a trace.
The only thing that was left, was a note with three phrases.

The Dead One
The Tree
The Wish

Markus will offer them some food as a thank you for being friends to his brother (as he is a great chef).
Characters can also visit the grave of Diuna at Wolf family home.
When they go there, Bard will show up out of nowhere.

"It was impossible to help her in any way", he will say.

He then will take his violin, and will start to play some song that is sad at the beginning but turns into something that would remind them about Diuna, a sweet melody awaiting brighter future.

Components

Hooks

Viktor promises quite a nice sum of money for completing his jobs.

Backdrops

Locations

Viktor Wolf's house
Most of the events in that side story start here. Additionally, characters can find some of the Viktor's research notes that can help them get to know The Pit a little better.

The Ruins
Ruins of old high school, where most of the combat could happen.
Things Viktor looks for are mostly located here.

The settlement these events happen in is unspecified, however, they should happen in one of the more populated and advanced cities. Not in The Depths and not in The Surface.

Plot type

Side Quest/Story

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The Actors:

The characters (either written ones or PCs).
Viktor Wolf and Diuna.
The Bard
Viktor's brother, Markus