Background info on your character: [canon history/background and your character's personality, please!]
Personality: Stein sees the world as his personal laboratory that he gets to fuck with and the people trapped in it are therefore his test subjects, himself included. He basically has a hard-on for dissecting anything of interest that stupidly wanders into his clutches. Oh and if you think it's a new thing? It's definitely not, because he used to be a hella creepy child too and he pranced around harassing his classmates and cutting open his partner while he slept. Though judging from his... Special appearance, he messed with himself just as much, giving himself a good couple of scars and a both that sticks through his head that he can turn whenever he feels like it. Even though it's pretty obvious that he's something of a sadist, his dissection obsession is more FOR SCIENCE than a desire to hurt people in the most agonizing way possible, but if you find yourself on his bad side, you're fucked anyway.
It's fairly obvious he's insane, though he has his good days when he seems more "really fucking weird" than "belongs in a padded cell" but they don't last. Stein also starts hallucinating with growing frequency as the series goes on, with his reactions to the things he sees ranging from complete terror to lashing out violently. When he's in one of his crazy moods, he flips from "curious and creepy" to "dangerous psychopath who couldn't care less if he tried". Not to say he's not always a psychopath. Stein never bothers hiding the fact that he doesn't understand most emotional responses past a clinical assessment of them. When he was younger, he was more amoral than he is now, though eventually he managed to have some semblance of kindness nowadays, as evidenced by his desire to protect his students from most kinds of harm. With people he likes (mostly just Spirit), he's actually sort of snarky and likes getting a rise out of them, for example calling Spirit an idiot and doing what he can to scare the living daylights out of his students for shits and giggles FOR SCIENCE.
tl;dr - He's batshit insane
History/Overview: According to TV Tropes, Soul Eater is "clearly Bleach on LSD". Pretty much, these kids who look about 15-ish go running about to collect 100 souls from the forces of evil so they can either be cool, surpass god, be like their mother, or for no reason whatsoever other than to get the best weapon out there. Oh and they have to balance doing this with schoolwork. Never fear, though, this isn't like Sailor Moon where shit be secret, yo; their teachers do the same exact thing and pull off Big Damn Heroes shenanigans when the kids are in a bit too deep.
As for Stein himself, he grew up at Shibusen, the school run by Shinigami-sama who's the guy who funds this whole evil-soul-collecting business, after his parents died when he was just a depressed-looking little kid who liked to smile awkwardly and cut open his fellow students. He and Spirit worked together for about 6 years before Spirit's now-ex-wife told him that those scars he woke up with miiight just be caused by the psycho he lives with. So he and Spirit broke up went their separate ways, and Stein pretty much became a recluse and messed around with various scientific abominations, including making one of the teachers at Shibusen a zombie.
Then, after a fight with Maka and Black Star, it's revealed that Stein's actually a side character rather than a Villain of the Week. And then he becomes a teacher and acts as a mentor to his students, especially Maka because they can both see souls and use scythes (though later Stein also uses Marie as his weapon, who's a tonfa).
After much plot, Stein goes a little bit loopier-than-normal in the head and pretty much disappears for the rest of the anime because he was damn near catatonic and decided to run off into the sunset with Medusa until he got better. In the manga however, after he gets better, he gets accused of murdering Marie's only hope for a husband even though he'd locked himself in his house at that point, so he goes on a quest to clear his name and goes back to kicking ass and taking names.
Sample post:
Well this is certainly a much nicer hallucination than usual... Not every day I get to picture myself on an island rather than somewhere horrible. I must admit, I like this one. Setting myself loose on an island with who knows how many rare or unknown species? It's almost like my mind is starting to pity me. Maybe next time Medusa shows up behind me, I'll actually get laid.
I wonder if that last fall is actually what did it? It was only a matter of time before something happened, I guess. Should have taken out those doorstops while I had the chance. Oh well. Now that I'm dead, maybe I can haunt Senpai and keep him out of trouble for once.
Though, I don't feel especially dead and no one else seems to think they've died either. If only I could see my own soul right now, then I'd know for sure. Such a shame, such a shame... I suppose I'll just need to take a look and make sure my heart's still beating to make sure! Does any one know if there is a hospital somewhere? I don't want to start the operation without knowing I can find some stitches afterwords.
A list of things your character might have on them after they got snatched up and put on this island:
A scalpel, a pack of cigarettes, a book of matches, and his chair.
If you're applying for a first character, tell us what Island wants the most, to show us you've read the rules: ...Well technically I've been here before, but. Yeah. Bonsai, koi, Aussieland