Demon Contract Deku AU
The bullying and stuff all still happened, but the whole sludge villain incident happened a year earlier. But, this time, All Might was more responsible about the villain, so Bakugou was never attacked. An organization that experimented on quirkless kids targeted Midoriya. Now, Inko was a witch, and had taught Midoriya how to summon demons. However, Inko was shot and killed before she could do anything, and Midoriya didn't have immediate access to anything he needed and being a scrawny, weak, quirkless boy with no weapons or combat experience, he was overwhelmed quickly and taken to be experimented on. All of the other experiments, who had been much younger kids, had died already. So Midoriya was alone. He was tortured and experimented on. The experiments didn't do much to him besides cause pain. The person experimenting on him got angry that nothing was working and took that anger out on Midoriya, injuring him. He was taken back to his cell without medical attention, them having decided that they would come back and get him the next day: perform more experiments if he was still alive, throw his body out if he wasn't. However, this gave him access to what he needed to summon a demon, and he did so.
Said demon being Shinsou, a demon who had originally been a human. He died recently, and Midoriya was his first contact. Their deal was basically that Shinsou would get him out of there and protect him, would not hurt him, and when Midoriya died he could have his soul to do with what he wished. There are other things humans can offer demons for contracts, but he didn't exactly have much to bargain with. Midoriya becomes a vigilante, trying to make sure that no child goes through what he went through. Shinsou doesn't get much of an explanation for the situation he found Midoriya in, until the people who were tormenting Midoriya nearly recaptured him, and Midoriya had a breakdown.
Through being a vigilante, Midoriya met Aizawa. Aizawa becomes fond of Midoriya, and becomes like a father figure to him. Midoriya gets caught eventually and Aizawa and Mic adopt him, then Eri and Shinsou (when they find out about Shinsou). Mic is like Shinsou, and Aizawa is his contract. They struck up a deal similar to Midoriya and Shinsou's.
Demons can't usually die permanently. They also age while on Earth. Also, queer platonic TodoDeku and brotherly ShinDeku.