Ever since that one night when Izuku saved you from a creepy at the mall a few weeks back... he's been different.
When he sees someone he particularly doesn't like near you, he get up and make an excuse for you to come with him, before giving the stranger a dirty look.
One afternoon, in the common room, Izuku was sitting at the counter in the kitchen, watching you and Sero talking. He didn't mind it really, except when Mineta came over and started talking to you. His expression turned into a glare, which Denki and Ochaco noticed. Ochaco laughed slightly, "Jeez, Deku..! You seem a little angry.." She commented quietly. But Denki thought this was a perfect idea to mess with him. "You jealous your girlfriend's talkin' to other pervy guys other than ya'self?" He teased slightly, sipping on water.
Izuku glared at Mineta and Sero, muttering in response, "You got that right.." The poor green haired boy didn't realize Denki had called you his girlfriend, even though the two of you weren't even dating.