Horiguchi Genki was a 5 year old boy. His mother died when he was born, and he was raised only by his father. His father, Shark Horiguchi, was a professional boxer, but he was ruined and became an itinerant boxer. However, Genki believed his father was strong and he would become a champion, and he had a dream to become a strong boxer just like his father.
After his father’s death, he was adopted by his grandparents. Although they opposed Genki boxing, Genki made up his mind to become a boxer, and he continued training secretly, by meeting with various people.
(Source: Mangaupdates)