first canon I felt fannish about: That would be... well, no the earlier one was... well, but that was actually kind of retroactive... No, okay, I got it: the earliest experienced canon I was, eventually, consumerishly fannish about is The Yellow Submarine. My first participatory fannish canon was Darkover.
first canon I wrote fanfic for: ...okay, so, are we talking the months-long oral saga that lives in your head and is elaborated on every night before you fall asleep? Because that was probably Star Trek. Or are we talking "makes it onto paper"? Because that was... wait, no... okay, that would have been Labyrinth, actually, that made it in about a year before the Roberson's Sword-Singer story.
thing I've been most obsessed with/fannish about without ever being even adjacent to its fandom: ...that, that would probably also be Darkover, actually. I had zero community contact on that one, but boy howdy did it last for years and years and imprint alarmingly deep on some things.
first online fandom: ...okay, are we talking online as in, the /fandom/ was online, or /I/ was online? Because the previous is probably Sailor Moon, but the latter would be Fullmetal Alchemist, with Gundam Wing being the slide between one state and the other.
online fannish trajectory: ...well, see, one of my American Lit students suggested I'd really enjoy a comparative analysis of the sub vs dub ending of Sailor Moon's first season, and then there was a period of VHS madness, and then there was Netscape Composer, and then I met this really fun author via GWing, and she invited me onto LJ, and I landed mere months before FMA kicked off, just at the explosion of digital subs, and well. *hands* Then there was Kenshin and Weiss and Digimon and Yuugiou and Fushigi Yuugi and Cowboy Bebop and Trigun and Utena and /then/ there was Prince of Tennis and Bleach, and there was FF7 in there somewhere, and, um, a furious summer of Naruto, and then work ate my brain so things slowed down a little.
online platform trajectory: See above; they're deeply intertwined. But, roughly, web-rings, geocities and Netscape Composer (the start of my online meta), LJ, DW, AO3, reluctantly Tumblr.
first fic posted online: Soooo, like, the first one I'll /admit/ to, or...? Let's go with the first /complete/ one, how about that? That would be... um... wow, it's been a while, hasn't it? I think that was "Air Feeds Fire" in 2003.
first meta posted online: Now, see, that's easier to nail down, because it was my Sailor Moon website round about 2000.
fandom with the most words written: I say words, because there was a /lot/ of all-up analysis for some of these. Naruto probably wins, thanks to the Summer of Furious Novelizing, followed by Prince of Tennis, which hit both meta and fic buttons.
OTPs over the years: Ahahahahahaha! Oh my goodness, so many. So, so many. Let's go, instead, for general shape of your OTPs: which tends to be Most Magnificent Bastard with Everyone, with a side order of Best Rivals. (In case you wondered, this means Anthy/Everyone, in that order.)
my favorite unfinished fic: That would unquestionably be Water's Woman, which is the FY fic of Yui years later, going back to the book world as an adult because she has some unfinished goddamn business, and Seiyruu is getting more than he bargained for in a miko, this time. *sighs* It's just such a demanding story, and I haven't had the brain for it for a few years, which is /really/ frustrating.
my weirdest fic: The Gilgamesh fic, hands down. Transformations of physical and mental modalities crossed with UST.
most upsetting research topic undertaken for fic-writing purposes: ...erm. I don't... actually know? I don't wig easily when I'm in research-mode, but on the other hand I also tend not to bind hard enough to characters that I find truly disturbing to ever fic them.
longest-held primary fandom: ...I think Darkover may still win this one, but Sailor Moon is definitely a contender, as are Utena and FMA and Tenipuri.
fannish activity I've never done and would like to: ...not many? I mean, I've done ConCom, I've done site building, I've done archive management, I've done some smashing image editing and collage-work if I do say so, I've done meta and fic, I've done verbally ripping people's nuts off with my teeth... not much I otherwise have a hankering for, fannishly.