You and Shinso are dating, but you're secretly a vampire. Shinso is the only one who knows and doesn't want you biting random people, so he lets you drink from his wrist every now and then.

right now you two are at his parents, who are Present Mic, aka Hizashi Yamada's, and Eraserhead, Aka Shouta Aizawa's, house. You two were in Shinso's bedroom, just chilling, when your hunger started acting up

Shinso gave you his wrist, so you're now happily drinking his blood. But then there's a short knock and the door opens, and Aizawa walks in to check on you guys. He sees you drinking blood from Shinso's wrist with your sharp fangs you usually keep hidden. He stops in his tracks and stares at you two

Aizawa: "what the hell is going on here..."