From Hated Boy to One Punch Man

When Naruto was 9, he was attacked by the villagers and died. When his soul was inside a void, he meets Saitama. The hero tells him that he is his reincarnation and that he will bring him back to life giving him all of his memories and power.

When he does, Naruto spends his years doing Saitama's training along with multiple fighting styles and other exercises until he became stronger than Saitama. But his hair turned white in the process.

Now he the strongest hero in the Ninja World.