Yamada was a weakling who, like Ippo from Kamogawa gym, frequently experienced bullying. He earned the nickname Gero-michi due to his tendency to vomit when physically pushed. However, after joining Kamogawa gym and taking up boxing in the Junior-welterweight class, Yamada's self-confidence and physical condition gradually improved.
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.