MC is reborn as Izuku Midoriya with the intellect of Tony Stark / Or there doesn't have to be a 'reborn mc', Izuku Midoriya could just be super smart.
As a child Izuku has shown his genius mind and started a company at the age of 10 which is managed by his mother. (The Company could be anything from technology to foods etc)
MC will be smart but not a hero fanboy, he uses his higher intelligence to gain an advantage at anything he does.
Izuku doesn't end up getting One For All and insteads becomes Iron-Man.
Thanks to the company he has created he build his own suit along with the AI Jarvis.
You can have him finish building his suit at around age 13.
Since he doesnt have a quirk he realises that he wouldn't be able to get into the Heros Course and isn't interested in joining the Department of Support since he doesn't gain anything from it.
He goes out and fights as a vigilante and doesn't get caught till he is around 15 (UA Age) You can have the heros ambush him since he would be an illegal Hero.
After he is caught he announces himself to the public as Iron Man and the CEO of company ???.
After the police/heros realise that he is only 15 they give him a chance to join the Hero's course.
From here on you could follow the original plot of the anime and changing it to match the plot of the story so far.
Things to point out.
1. Due to his intelligence he graduated his middle school and high school education at an early age. (Doesn't suck Bakugos dick everytime he sees him.)
2. Is Rich so write about how he got rich and how he invented the products he sells (He could create a product that could allow civilians to protect themselves from villains)
3. Due to his status you could have him get into a relationship with Momo since her family is rich and would most likely have good relationship with his company.
4. Use Jarvis to scout for villain reports/hacking into databases to gather information.
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AN: Anyways I hope someome uses this idea and adjusts things to make it even better!