The guy reincarnated as Shinra Kusakabe In MHA. (I don't even have to explain how strong this guy is)
You can make him slowly evolve his quirk.
1st Gen
2nd Gen
3rd Gen
Then the super speed Shinra (I forgot the lore about his power)
Or you can make it as a template.
So the mc has a chance to access the other powers in Fire Force.
The plot can be he is shunned because as soon as he awakened his quirk he burned their house and he smiles as it happened.
Integrating the burned people in MHA is hard but the mc could try and make his own agency called the fire force. And because the templates can be given to others he could essentially grant other people quirks and could just say that it's a part of his quirk to hive others fire like quirks or more like awakening their feiry potential, you decide.