My main obsession would definitely be my fictional husbands (of whom there are many) and my fictional wife (of whom there is one). They just make me so happy and I love them all so much.
I like to collect merch of them when I can
(and when it actually exists at all ;-; ) as well as whatever official art of them I can find. They just bring me so much comfort and have really gotten me through a lot.
Aside from that, I really love fiction in general, especially books and video games. I've been a fairly serious bookworm ever since I was little, and over the years I've managed to collect enough books to fill one bookshelf taller than me and part of a second. I grew out of liking a lot of the novels I read when I was younger, and it's mostly shonen manga now, but I do have some manga from other genres, some light novels, some of the Steven Universe and AtLA comics, artbooks/fanbooks, and a handful of non-fiction books as well.
I don't have anywhere near as many games in my collection by comparison, but whenever I really enjoy a game I often try to play to 100%.
(Or close to it, at least—for example, there's still a lot I want to do in DQXI S, but the horse racing accolades are definitely not a part of that.) I do full replays of some games on occasion too, but even if I don't go quite that far, it's rare that I won't at least complete the story + any post-game story content once. And I'm always on the lookout for new series or games that I think I might like—plus, I'd also really like to write my own books (and
maaaaybe make my own games) someday.
Also, in the past I was super obsessed with Naruto and later, Undertale. Like, I was teaching myself all the ninja hand signs, and I would try to learn every little easter egg/hidden conversation/fun value quirk there was to be found in Undertale. I do still like both of these things though, even if I'm not focused on them to that degree anymore.
Although I never actually finished Naruto. I swear I'm going to someday.