Todomomo-

Totally Momo. She probably got flustered by someone and thought the best way to stop feeling so weird was to confess

Kirimina

Totally Kiri. He kind of had a crush on her for a year and decided to Man Up and ask her out

Miruhawks

Hawks did it-

IidaMei

Mei probably let it slip and Iida was like 0-0
And she repeated herself with no shame

Kamijirou

...

It was Kami.

Dabi x Toga

Totally Toga.