Yamada was a weakling who, like his Kamogawa gym sempai Ippo, was often bullied. He was given the nickname Gero-michi because of his tendency to vomit whenever pushed physically. However, after joining Kamogawa gym and taking up boxing in the Junior-welterweight class, his self-confidence and physical condition steadily improved.

Spoiler

After developing a bond with Ippo, he moved away and joined Hachinoe gym. There, he shaved his head and is eyebrows. And gained the nickname "Hammer Nao" because his fists were like hammers. From there, he dropped down to the Featherweight class and challenged Makunouchi Ippo for the Japanese Featherweight title. He lost by two-round Knockout.