[2][3] Watanabe, who fought only in Japan and South Korea, was one of the first World super flyweight champions, as the division was relatively new when he was crowned.
With a background in Shotokan Karate, he started his professional boxing career with a three-round knockout over Keiza Miyazaki.
One of the fighters he beat was Tito Abella, who by then had been ranked as the number one Jr. Bantamweight challenger in the world.
Watanabe's remaining fights of 1982 were title defenses against former world champions, Gustavo Ballas of Argentina, knocked out in nine rounds, and Shoji Oguma (former two time world Flyweight champion), beaten by a knockout in 12.
In 1984, Watanabe disposed of another Venezuelan challenger, Celso Chavez, by knocking him out in 15 rounds.
In 1999, Watanabe was spotted at a Seoul activity honoring Asia's greatest boxing champions, alongside Fighting Harada, Jung-Koo Chang, Yoko Gushiken, Sot Chitalada, and former rivals Chul-Ho Kim and Poontarat, among others.
After being released in 2004, he was arrested for blackmail along with Kenji Haga, ex-actor, and a yakuza of Yamaguchigumi, on 30 June 2007.