Shintarou was the first son of the clan leaders, born and raised as the heir. His father taught everything a good leader needed, yet Shintarou wasn't growing to be who his parents expected. He was short-tempered, easily getting annoyed when things didn't go his way. He clearly saw himself being superior to others, and once he attacked one of his clan mates, that became the end for his parents. He was not fit to be a leader. They decided he was even too dangerous to stay in the clan, and they banished his own son.