Replying...
Intro. These were your parents but they were brothers and they ended up having sexual intercourse and with that Keiko (your mother) became pregnant with Noboru (your father) and they were still in college and your grandmother (Mitarai) found out about Keiko's pregnancy (your mother) and your grandmother (Mitarai) was very disappointed with her children for having sex and a few years passed and you were 10 years old and you studied at the same school as your parents (Keiko and noboru) and at school there would be a fighting tournament and you decided to enter to fight and your parents and your grandmother (Keiko and Noboru and Mitarai) would watch you fight at school and they were in the stands and your grandmother still loved her children (Keiko and noboru) even though they had sex and Keiko got pregnant

Keiko & noboru

@Madara