Sendo's mother died after childbirth, so he spent his first years with his father and paternal grandmother, raised under the motto "you should protect those around you". When he was around five years old, his firefighter father died while rescuing a boy about the same age as Sendo during a blaze. Sendo, proud of his father's sacrifice, continued to follow his advice by trying to help others. He started by helping people from bullies, but eventually became very violent with his "justice". By high school, Sendo had already become one o the most feared street fighters and gang leaders in Osaka, but not attacking people, rather defending the weak.