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.

Midoriya Izuku was born with a quirk: the ability to summon and bind demons from an alternate plane to do his bidding. With only a few days left until the UA entrance exam and still no offensive-type demons in his arsenal, Izuku makes a desperate attempt at summoning one corporeal, a feat he had never before attempted. He'd say it was a success but, he doesn't actually know if it'll be more a help or a hindrance. Especially since Bakugou Katsuki is, well, kind of a shit.

Sidney is not living out a Hellish version of The Little Mermaid, except for the parts where he kind of is.