As a boy Izuku faced many rough things he didn't deserve, starting with serious bullying and low self-esteem stemming from his Quirkless nature.
Tensei Iida was a successful and popular pro hero who did many things right, but Stain the hero killer still targeted him and nearly killed him on a one-sided fight.
Eri was just a kindergarten-aged kid when she ended up in Overhaul's custody, and she endured painful experiments and procedures to weaponize her remarkable Quirk.
As a child, Tenko was a happy, optimistic boy who adored heroes, much like Izuku Midoriya. However, his stern father Kotaro harshly rejected that idea, which alienated him from his son.
Dabi is one of several My Hero Academia villains who grew up totally innocent until disaster struck, which was not their fault. Dabi was once Toya Todoroki, Enji and Rei's firstborn son, but he was born with fire powers that he couldn't possibly control.
Born as Manami Aiba, La Brava faced total social ostracization in school, and felt heartbroken that no one would be her friend or even look her way. Discouraged and bitter, Manami retreated inward and became a shut-in until she sought out Gentle Criminal to become his sidekick.
A noble boy who trained incredibly hard to master his Quirk and become a melee powerhouse. Mirio deserved to master his Quirk and become a star UA student, but he did not deserve what happened in MHA Season 4.
Rei openly objected to her husband's methods, but there was little she could do, and she couldn't easily leave their twisted Quirk marriage, either. She wanted to be a normal mother to normal children, but "normal" eventually went out the window, as the burn scar on Shoto's face proves.
In his youth, though, Hawks suffered and didn't have a normal childhood, a fate he did nothing to deserve. Hawks's parents were impoverished and abusive, and he never saw his father again. His mother was unable to raise him correctly, so Hawks was raised by the Hero Public Safety Commission's staff and become a powerful tool of justice.