Well if he's just not into, he'll probably never understand. But if he's seriously into gaming, perhaps you can use that as an analogy.
Anime and Fanfics are your video games!
Plus as you said, he knew what he was getting into.
I always say that to hubby, and he always replies, but I didn't know HOW weird you are! LOL.
I say that, but since he's an anime fan he's cool with my obsessions, pretty much anything I own that is anime related, was bought for me by him.
Last year for my birthday he finally got me that Kotobukiya Sesshoumaru I wanted to match InuYasha and Kagome.
Actually, my first Christmas spent in the U.S, my favourite gift from him, was InuYasha fanart he'd commissioned from an artist on deviantart.
Actually sweetie that he is, he later commissioned an artist to draw fanart related to an InuYasha fic I was writing at the time.
I'm super lucky, hubby and I have a ton of interests on common, so we don't often run into this problem.
Except football and baseball, I'm probably never going to like those sports. He did manage to get me crazy about hockey though, so I guess that's a compromise