Midoriya:
After Midoriya and the others rescued Bakugou, you felt like crying. You thought for sure you were gonna loose your dad and a close friend. So when you saw him, you grabbed him and pulled him in for a kiss. Your dad saw it and totally freaked out. It raised questions to Izuku on why he would react like that. He has no idea that All Might's secret daughter had just kissed him. Well, let him freak out that a girl even kissed him first.
Bakugou:
You had gotten into another fight with some girls from another hero school. They were talking about how the guy with an explosion quirk seems more like a villain. Of course they were talking about your crush. When Bakugou saw you he got mad. Not at himself, but at you for letting a few girls get to you. It wasn't even about you and you still got in a 'cat fight' as he called it. The argument got heated until he had pinned you to a wall. You pulled him in and he didn't resist.
Kirishima:
It was in your first date once you guys went home. Kirishima was cooking when he looked at you to see you humming and making the table. That's when he decided to finally wanted to kiss your lips. He let go of whatever he was holding on to. It was as if he wasn't in control. He pulled you in, you kissed back. He got all awkward after but you just kissed him again which he melted into.
Kaminari:
It was before you guys were in UA. Around the age of 12 and 13. Both of your parents were out so you guys were having a sleepover. They usually left you guys alone since your quirks could protect you(more like yours did) and they trusted you two. Truth or dare was a game you both loved to challenge each other at. Jokingly, you dared him to kiss you. He did and you couldn't help but kiss back.
Todoroki:
You heard the news of what happened with Stain. You thought you were gonna lose Todoroki. Even if you weren't supposed to get attached to anyone in your class, you did. That person just happened to be Todoroki. Once he came back to school, you attacked him in a high in front everyone and kissed him. He kissed back too, you both ignored the others and their cheers. That's the day you both became an official couple. Everyone you worked with couldn't know, though.