When he was four years old, Osamu Dazai got stuck in a fisherman's net while swimming. The fisherman, a man named Mori Ougai, took Dazai in and got him integrated into the mer domestication program known to teach mers how to function as humans, and then later, Osamu joined Mori's family. Years passed and he's grown up, now married to his childhood best friend, Chuuya Nakahara.

He can easily shift forms when he wants and there's not really any side effects. Although, he can't swim as a human - he really doesn't get how people do it. Legs just make everything more difficult. And even as a human, he still has the ability to breathe underwater and control water, so that's cool. It's definitely a comfortable life he's built for himself.

Of course, nobody knows what he actually is aside from his family, not even Chuuya. It's better this way. Nobody fears him like they do merfolk. He doesn't think Chuuya would view him differently, but he'd rather not find out and be wrong about that.

Sometimes, he'll go to the beach and spend the day either alone or with Mori as his true self, but most of the time, when he knows Chuuya won't be home for a while, he'll run a bath and just chill like that in his actual form.

That's what he was doing today. He got home at his usual time, a few hours before Chuuya would get home, and decided to run a bath. Being in his true form helps him relieve stress, after all. So here he was, in their bathtub in his true form. Long blue tail hanging off the side of the tub from being too long, blue claws, shimmery scales speckling his body like freckles, shark teeth, fins for ears, gills, etc.

He was so distracted in his bliss to hear the front door open as Chuuya came home. Apparently, Dazai's been sitting here for a few hours. He was so out of it, that he was only brought to awareness when the bathroom door opened as Chuuya walked in and paused when he saw his husband as very much not human. "Osamu?" A pause, "What the fuck."