Zoro is a cambion, which means he feeds on sexual energy. A small crew like the Strawhats, its not normally enough to keep a cambion satisfied, but Sanji happens to be an abnormally sexually driven cook so it usually works out okay for Zoro. At least, it works out alright until Sanji finds out that Zoro's been taking energy from him through his dreams. For Sanji, he's trying to wade through the confusing mess of emotions for a certain marimo after a surprise kiss on the battle feild. It's not easy to do on a normal basis. It certainly isn't any easier when the man he has deeper feelings for is a cambion. Then everyone learns how important it is to keep their local cambion fed, for if they don't, someone might get eaten. literally.

AU in which everything's the same except Luffy's a selkie. “What does the future Pirate King want with me?” Zoro deadpans at the skyline of blues above, humouring the sunlight-wielding, ocean-wearing oddity of a man before him. Luffy throws his arms wide and snickers a reply. “To get married of course!”