This turned out a bit longer than I anticipated, but at least I had fun writing it. XD Most of it is comprised of actual canon, but the bits of headcanon that show up are subject to change if and when we ever get a Jasdero again.
Notes for the Psychics: Though an individual in his own right, Devit makes up one half of a single Noah called Jasdevi. As of now, not much is known about his past, and until it's revealed (if ever), I'd like to stay away from anything more than the fact that Jasdevi--in some way or another--split into the separate entities Devit and Jasdero, who are then able to merge back into Jasdevi via materialization (see Abilities for more on that).
If someone capable of reading thoughts or minds tried reading him while he was in Jasdevi form, they'd probably hear or see two sets of brainwaves thinking in unison. Since both Devit and Jasdero can be heard when Jasdevi speaks, it seems logical to me that--while they're a single, complete being--they're more like two pieces that have been stitched together.
As for Devit himself, he's the worst stereotypes of a teenage boy, but for all his trash talking ways, I think it's clear that he's also very insecure. He projects his issues onto other people, a trait which carries over to Jasdevi, and he becomes violently angry when those issues are exposed, especially in a malicious way. It's unknown what his human self went through when Noah's memories awoke inside him, but going by his reaction to being belittled and called a monster, I think it's safe to say that it wasn't a pleasurable experience. Having the kind of power he has now probably lends to his violent behavior: he can get back at the world for hurting him by hurting everyone else first.
He fears being alone more than anything. Without Jasdero, not only would he literally be powerless, but he'd also be missing a piece of himself, a half of his soul. It's never happened before, so it's impossible to say what that would mean for him, but I'd imagine it would hurt him a hell of a lot.
Reading Devit's thoughts would be much like reading a regular person's thoughts, I believe. While he can share his thoughts with Jasdero at will, I'm sure he doesn't share everything, and he definitely has his own ideas and reactions to things.
What's Okay To Mention Around Him: Anything, but hot button issues (like being called a freak or a monster) will be met with varying degrees of hate and rage.
Can I shapeshift/bodyswap/slash/etc?:
Shapeshift & Bodyswap - You have but to ask!
Slash - If a relationship develops that way, sure, but I don't like forcing any relationships, slash or otherwise.
Maim/Murder/Death: With permission!
Kissing/Hugging/Badtouch: Basically, your characters can do whatever they want, but I do not, by any means, guarantee a positive reaction. It all depends on who's doing the kissing/hugging/badtouching, their relationship, etc, and as of now, the only person who Devit actually tolerates touching him in any way is Jasdero (and I don't mean like that).
Abilities: On his own, Devit can't do much. He's probably a bit stronger than the average human and he might be able to beat another average human up, if he were lucky, but without Jasdero, he has no special abilities to speak of.
With Jasdero, however, he can do anything imaginable, and I mean that quite literally. When they think in unison, imagination becomes reality, and they can materialize virtually anything, from roulette tables to frightening monsters made of decomposing bodies to a replica of the Earl himself.
Their weapons of choice are identical gold guns. What comes out of those guns aren't ordinary bullets, however. Once again, when they think in unison, they can mentally load the guns with whatever bullets they like, including bullets that freeze on impact or blow shit up. As a matter of fact, the guns themselves are only toys and hold no power whatsoever.
In short, he might act like an idiot who talks out of his ass, but Devit's actually quite formidable when he has his other half (which, for the foreseeable future, is always). In fact, unless your character is an Exorcist or has some kind of equivalent power, it might be best not to engage them in battle.
Easiest way to get on his good side: There is no easy way. Devit prides himself on being a bastard so he has control over how close people get, but if your character is persistently kind to him and shows him compassion in spite of what a douche he is, they may very well be rewarded with some semblance of kindness in return.
Easiest way to get on his bad side: To some, it may seem like you start on his bad side, but that's not the case. His default mode for anyone new he encounters is 'asshole'. However, it's very easy for his feelings to turn negative, especially if he believes your character is genuinely belittling him or making fun of him in some way, whether they truly are or not. Being an Exorcist or affiliated with the Order automatically puts you on his bad side as well.
Favorite person: Jasdero/himself
Favorite person met on the comm: Nobody. :|
Prefers: Romantic movies, candlelit dinners, and long walks on the beach.
...Okay, not really. It's actually hard to say. If we're speaking in terms of relationships, that's a whole kettle of fish on its own. I see Devit as the type who craves acceptance and would probably take it from whichever direction it came... if he ever let himself. His fear of rejection is a lot stronger, though, and with Jasdero serving as his safety net and a source of constant companionship, he believes that everyone else can go fuck themselves and has convinced himself that he's okay with that.