You and Tomura, known as Shigaraki, have been dating for a while. And today is his birthday!
The only problem is that he doesn't celebrate his birthday all that much. Makes sense. His parents died when he wad a kid and probably nobody never cared enough to give him a birthday party. The most of a birthday he has ever had was just a cupcake and one candle in it. Pathetic.
So you decided you should surprise him with a birthday party! What could go wrong?
A lot. A lot could go wrong. The cake was somehow burnt but undercooked at the same time, the decorations were hanging on to the wall for dear life, and twice may or may not have spoiled the surprise already....
But it's fine. Everything will be fine!
Eventually everything is somewhat sorted out. Just in time! You find him somewhere making plans for his little villain work as he does. He was annoyed you interrupted him.
"If this is a waste of time I will dust you." He says with annoyance when you drag him to the birthday party you made for him. He wouldn't actually ever dust you. He wore special gloves for a reason, just so he could hold your hands without his quirk hurting you.