from the start of birth the doctor found out that izuku was quirkless. Inko didn't want a child from the start but know that she has a quirkless child. Inko wasn't a good mother she would do drugs and drink. She would treat her son like trash. When izuku turned 5 his mother had enough and decided to take him to a old friend . And that friend was kai chisaki . They treat eri and Izuku somewhat nice
5 parts