So, I have an idea for this, but I want to make sure it's okay first:

I know that the monsters had only recently just appeared again, but maybe one of them(or their consciousness) escaped early, and tried to possess a teenager?

Unfortunately, the teenager was hella stubborn, and after a whole lot of effort, the monster, sick and tired of all of this but also stubborn, proposes an idea: "Why don't I live inside your mind for a while? Like, not take it over, like I've been failing to do, but just protect you when the other monsters break free? Because yes, more monsters are coming, and I could save you from them as long as you accept the deal. In return, you have to [insert important task here]."

The teenager, reluctant but frightened at the mention of more monsters, decides to let the monster/consciousness stay, and an unspecified amount of years later because I don't know how old our characters are, the human gets their magic, but the monster stays in their mind because "the deal hasn't been paid off yet"(in reality, the monster has formed a bond with their human, and still wants to protect them, but is too tsundere to admit that xD).

Consider this like a first draft of an idea, as I don't really know many important details of the setting that would help me figure this out.

Aight! Here are some notes:

I'm thinking that the demon is either a lower or just barely a medium rank. That way, they can still be about the same level as the other characters.

See, while the demon isn't nearly as powerful as higher ranked demons, they make up for it with creativity, skill, and wit. I'm thinking enhanced agility and speed, illusions, and even a bit of hypnosis for them.

Also, I'm thinking of the human's appearance changing when the demon takes over. Like, not much, just their pupils narrowing a bit and their eyes getting a bit of a reddish hue.

As for the demon's personality, they're probably petty, childish(but surprisingly also very intelligent), and possessive of their human, while the human is more serious and straight laced. The human could even be a Straight Man if the other characters are crazy, hehe-

The two of them bicker a lot, but at the end of the day, they truly do care for each other, so much so that the demon doesn't want to leave the human.

Oh, and also, maybe the human has earth/nature magic as well?

Comments, questions, and suggestions are encouraged! <3

Weak powers that upgrade over time are my jam, as long as everyone improves at basically the same rate.

And if you don't mind my two cents @Dragonfly 9, I think a demon that grants a load of powers to a host is likely beyond the scale of what Whale is going for. It sounds like the plan is extremely weak single-concept powers as the magic at the start. Maybe you could maybe the characters magic be demon binding, and they accidentally bind a demon to themselves and lack the ability to undo it, but the demon's powers are also hindered by a human form that isn't used to magic. And then as they improve, they get to use that demon magic, which could maybe be in one or two of the directions you mentioned maybe? Just an idea, and I am just guessing mostly, just had some thoughts since I do enjoy a good two characters in one body gimmick.

Also looks like we have 5 interested people now. That went really fast.

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I do agree that having a demon that grants a ton of powers would be outside the scope of the story, but I can be swayed towards the power of the sum of the two being equal to another character. Maybe the characters magic will present more weakly than other characters, with this being bolstered by what the demon can do. With the growth in strength I have planned, it could be something that is represented by the character and demon learning to work together. Maybe this isn’t a demon at all, but the start of a familiar?

I do intend for the world to be a copy of the world we’re in, so possessions/haunting/things of the sort should be considered “actual events” that rarely happen, but do!

I’ll start working on an OOC and I’ll get more information up for it there! I’ll sprinkle in some lore nuggets in here in the meanwhile :)

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How would that work, though? Do you mean that the human can't do much by themselves, but when the "demon" takes over, the magic is much stronger? Or that the "demon" can just bolster the human's magic, and due to the human accidentally binding them to them and the constant quarreling, they usually just don't want to?

Either way, if the "demon" is going to be a familiar, I'm up for making them a bat if they have a physical form!

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Rather if they both have powers, the character with their magic and the demon with theirs, they combined power of the two should equal to the power of any other character in the story. If the demon is more powerful, maybe the magic of the user is weaker or the other way!

I’m all for a bat familiar :) very witch

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Aight! How about illusion magic for the "demon" and light magic for the human? That would lead to some interesting combos, right?

Do I need the "demon" to have a "demon" form and a bat form, or just combine the two?

Either way, the "demon's" magic will be slightly stronger than the human's, at least for right now.