As Izuku and Momo saw the other side of what hero's does and they and now they had to choose after what they witnessed and now they went dark. As Nezu knows that they know the secret of what him and the other hero's does he wanted to maintain the 2 so they won't say nothing and one day after 5 years he find them and they refused to be a hero to be kept quiet he told would tell them they would be a villain which they had no problem which lead to AFO getting the both as Nezu was stupid enough to bring him to them.

Ship

Izuku x Momo

Both Izuku and Momo dumped Ochako and Shoto as they were with what the hero's done.