The story of What If: Shingen have a another son before Gun born. The first son who's actually look like his father, and that's is Izuku, who has been through a lot after being diagnosis as a quirkless. Inko is being concubine at the Yamazaki Family. Shingen and Her have a night and create Izuku which where he born but Inko have a plan after she gave a birth. She leave at the clan such as the fear of her child being used by the clan for generation and more in Yazuka Stuff, she feared her only son would be killed at the end. So she left and Shingen didn't find her or even concerns hunt her for his child. At the time Passed Izuku grew up being different such as he know there's something on him because of his black eyes, such as it leads on the bullying but it's doesn't matter to him because he always fought back so he's not easily getting beatin. As he grew up and got the UA where his dreams come true, but eventually at the end it didn't happen because of the incident that being framed up of being traitor such as he thrown at the Tartarus where he become more strong and more. After few years. The LOV revealed the whole world that izuku is Innocent and they only frame him so the people lose trust to the heroes. At the end Izuku didn't even care and just went out to kill who ever stand on his way to finish this ridiculous Heroes and Villains war. He know the price and he will gladly pay for it. For the peace and the being symbol that it will not forgotten, no matter what. Sacrificing his life, eventually he died at the end while fighting AFO and Tomura Shigaraki AKA Tenko Shimura. Izuku thought it's the end but when he found that AFO has a last sleeves that his body is detonated by a bomb. He look at his daughter Eri at the last time before AFO's Body explode, creating a powerful explosion that everything on radius being burn into nothing. He accepted it even it's will cause him. After all this is the last duty of being Hero and being Father as well.