He was promoted to yokozuna simultaneously with his friend and rival Kitanofuji in January 1970 and the two men represented the dawning of a new era after the dominance of Taihō.

He was born Taniguchi Masao (谷口正夫) in Osaka, but due to the bombing raids of that city he was evacuated to Gamagōri (Aichi Prefecture) where he grew up.

In 1965 a change in the rules meant that wrestlers from the same group of stables could meet each other in tournament competition, and Tamanoshima defeated Taihō in their first official match.

At first, he was unable to reach a score in double figures at ōzeki rank, but his results began to improve significantly from November 1967.

Upon reaching yokozuna Tamanoshima changed his ring name to Tamanoumi Masahiro, taking his coach's old shikona surname.

Tamanoumi had needed an appendectomy since at least July 1971, but he felt the responsibility of a yokozuna's duties and had not wanted to withdraw from the September 1971 tournament.

After competing there taking painkillers and remarkably managing a 12-3 record, he went into hospital only after being an attendant at Taihō's retirement ceremony on October 2.

Sanshō key: F=Fighting spirit; O=Outstanding performance; T=Technique     Also shown: ★=Kinboshi; P=Playoff(s) Divisions: Makuuchi — Jūryō — Makushita — Sandanme — Jonidan — Jonokuchi