If the Free! characters had Tumblrs
water and swimming and the like (he once followed a blog with "watersports" in the url and was very surprised to find out it wasn't about swimming).
pictures of cats, nature, cats, humor, anime, other cute animals, cats, DID I MENTION CATS?
sports, fitness and a lot of black and white/negative and hipster stuff.
humor, horror anime, food porn and a shit ton of selfies. He sends Rei a lot of stupid anons, too.
anything he considers "beautiful" at the moment. He reblogs all the "science side of tumblr explain this" actually writing an essay explaining the thing because he'd totally do that.
muscles galore, but also fashion, anime and some yaoi.
he only made a blog to stalk Rin and send anon hate to Haru.
humor and poRN.
he's actually tumblr famous but nobody knows.