In lieu of any kind of real profile-esque thing, and because I'm terrified of contradicting myself somewhere in-game with a completely new character, here is a list of facts about Fabian! Random characteristics and memories that are relevant, parts of his childhood or adulthood, things that make him who he is, filling in some blind spots for canon, etc. I'll keep it up and add new things every time I learn them, and datestamp them whenever they're added, so that any curious followers can see when it's updated. :D
To any future typists of characters involved in some of these facts: everything involving your characters is obviously totally negotiable! I've tried to avoid involving other people as much as possible, but it happens, so I'm willing to be flexible if you don't like anything I've said about them. \o/
1. Fabian never played Quidditch, but Gideon did, and he did get a good amount in himself helping his brother practice. (He would probably have played Chaser, though he makes a passable Keeper as well.)
2. For the three nephews he lived to see to their fifth birthdays, he bought them all toy broomsticks for said birthdays. He would also have bought Bill an owl for his first year at Hogwarts, had he lived that long.
3. Fabian is bisexual, but leans very strongly -- almost exclusively -- towards women, to the point where even most of his friends and acquaintances assume he's straight. He'll happily take up the mantle of flirtation if a man addresses him that way, but he usually only initiates it with women.
4. He knew within five minutes of meeting Arthur that he was the right man for Molly, but out of brotherly duty, continued to attempt intimidating him and putting him through "tests" until Molly, exasperated, convinced him to just tell the man he liked him and approved of the relationship.
5. The Prewett parents were along the lines of a typical pureblood family, but not quite as fanatical about it as some of the others. They were never sympathizers with Voldemort or the extreme ideology of blood purity, but they were rather conservative and never really liked Muggle-borns or even half-bloods too much. As a result, even after years at Hogwarts, Fabian always retained a slight surprise when Muggle-born wizards or witches showed exceptional skill; once he left, he worked very hard to eradicate all traces of prejudice still remaining in his mind, and by the time he finished Auror training, he'd mostly succeeded.
6. Just out of Hogwarts, Fabian had at least enough maturity to recognize his own immaturity. Auror training was always the dream, but he spent two years on the Magical Law Enforcement Squad first, getting some experience and personal growth before he felt strong enough to go through Auror training. He was an Auror for four years before his death. [updated 7/28]
7. His older sister got married when he was fourteen, and he became an uncle for the first time at fifteen; by the time he reached majority, he had two nephews, and by his death nine years later, he had six. Despite all of this domesticity surrounding him, Fabian never had the urge to settle down so young. He might have done so a couple of years out of Hogwarts -- had it not been for the war, during which he quickly put himself in a position where anyone very close to him would have been in jeopardy. Not the best environment for picking up ladies.
8. Fabian's Patronus is a bobcat.
9. Fabian is right-handed, and Gideon is left-handed. As a result, when they're walking together, they tend to stand with Gideon to the left and Fabian to the right; when they learned to duel together, this is how they stood, too. It's one of the big reasons they're formidable dueling opponents -- when dueling together, they literally have no weak side. [updated 7/31]
10. Fabian's best subject in school was Charms, with Defense Against the Dark Arts as a close second. He occasionally had flashes of brilliance in subjects like Potions, because he's at his best when it comes to subjects that let him think on his feet. History of Magic and Arithmancy were always his worst, because of the concentration and planning required, and his concentration levels were never quite up to par for Transfiguration and Herbology (though he did manage to improve with time, especially after he realized his Auror ambitions).
11. Fabian's wand is oak and dragon heartstring, eleven-and-a-quarter inches (a little shorter than one would expect, especially for someone with such a wide wingspan, but it was the first one he tried, and it was immediately the one for him).
12. While Fabian is the youngest of his family (younger than Gideon by half an hour), being at Hogwarts made him settle into a protector role with younger students, and eventually younger Order members (as well as his small nephews). Merlin only knows where he gets those instincts, but they're deeply ingrained in him by the age he is now.
13. Fabian doesn't think he's ever been in love, but his past relationships have been so long ago that his recollections of his actual feelings are a little fuzzy. How will he know for sure until he has one again?
14. In general, Fabian trusts his feelings much less than his actions. He's sometimes very bad at even recognizing how he's feeling until he has some kind of physical gesture to confirm it. And talking about his feelings at all is anathema to him -- in his mind, people know how he feels about them, whether good or bad, through his actions.
15. Fabian's boggart, before his death, would have been the image of a dark wizard -- any dark wizard (Voldemort, as he rose to power) -- laughing at him, because it would mean, to him, that he had failed in some essential way -- failed to keep his family or friends safe, failed to fight to the best of his ability. Ever since returning to life, it would likely be himself, dead, because he's terrified of losing his second chance at life before it's figured out what it's for. [updated 8/2]
16. The Sorting Hat never really considered putting Fabian anywhere other than Gryffindor, although historically the Prewetts had been about half in Slytherin, half elsewhere. He did make a half-hearted attempt to convince it to put him in Ravenclaw, and for years to come told the story of how he was probably the only student of his year to make the Sorting Hat laugh uproariously.
17. All of the Prewett children got relatively normal first and middle names, because the family got rather tired of the more elaborate names that had been the family norm previously.
18. Speaking of names, Fabian isn't too fond of nicknames. He will accept "Fab" or "Fay," but he's not too big on either and using them in some kind of derogatory context may well get you hexed.
19. The one piece of canon we get about Fabian is that he wasn't terribly careful with his possessions. This is unequivocally true, unless the possession in question was something particularly important, with significant sentimental value. Otherwise, he reasons, they're just things -- all of them replaceable.
20. Fabian flirts, almost by second nature. He doesn't truly intend most of it -- it's just one of his best ways of communication. If he doesn't flirt with someone, it's either indication that he truly cares about them (though the flirtation does sometimes extent to them, too), that they're family, or that he really dislikes them. [updated 8/5]
21. He does want, one day, to settle down with someone permanently. He's always thought he would become the type of person who would want to do that, and somewhere along the line, he became one without realizing it. Once he recovers from his current bewilderment at his situation, he may consider seriously looking, because he thinks it's about time.
22. Fabian might not be certain about whether he's felt romantic love, but he does know that his entire conception of love was turned on its head and truly begun, for the first time, when he first got to hold Bill, within a day of his birth. His nephews and niece mean the world to him, and apart from hurting either them or his own siblings, there isn't a single thing in the world he wouldn't do for them.
23. Fabian lost his virginity at age sixteen, and had not slept with anyone for eight months before his death.
24. He has never really had any jealousy of or competition with Gideon; their entire lives, despite several minor blips, had been spent in amicable partnership. [updated 8/6]