It's a beautiful day in Japan, and a huge audience has gathered to witness "The First Strongest Hero Fighting Tournament". Miyake Masaharu is ready to begin the tournament, but is waiting for a special guest to arrive, when all of a sudden Miyake-san spots something off in the distance. Son Goku appears riding on Kinto-Un and he jumps off, landing in the area. After a quick jab and a kick, he's ready to take on all his strong opponents. Miyake-san tells Goku that he has been brought in to commentate, not fight. Goku decides that's fine with him, as long as there are strong people in the tournament.

Source: Kanzentai

Note: A special animated segment part of Nihon Ijin Taishou 2007: Rekishi o Kaeta Chou Erai Hito SP (日本偉人大賞2007 歴史を変えた超エライ人SP) that aired on Fuji TV.

Alternative setting: Dragon Ball Z