ANBU2

Obito is the captain of the ship called the Akatsuki, but he belongs to the fleet of the Uchiha with Madara as its admiral.

The rest of the crew are the other members of the Akatsuki and in this au they're more of a found family (as much as a bunch of lawless and ruthless pirates can be); they generally do like each other even if they don’t show it. Also Nagato and Konan are less insane because Yahiko is alive. They are the most feared pirate crew of the sea right after Madara's.

Kakashi is an abyssal mermaid/siren but because he's albino he's too noticeable and was used mostly as bait by the other sirens. That's why he eventually left them and tried to hunt on his own (to little success).

Obito meets Kakashi when he gets stranded on an island. After the events of the comic the rest of the crew appear and they capture Kakashi. He's brought on to the ship and into a water tank of sorts. When the Akatsuki discuss what to do with him, thinking on just selling him, he manages to make a deal with them: if he stays with them, he'll retrieve the valuables and gold that would be lost to the sea from the ships they attack and in exchange he'll eat the sailors that drown anyway. And of course, they're pirates (and insane), so they accept.

And now Obito and the Akatsuki have a simbiotic relationship with Kakashi. Along the way they end up liking Kakashi and of course at some point Obito and Kakashi fall in love.