His father was a construction worker who competed in amateur sumo tournaments. The young Mienoumi did judo in junior high school and was introduced to a sumo coach at Dewanoumi stable, but was initially rejected due to his short stature. He contacted the stable again a few years later, and this time was accepted by Dewanoumi Oyataka himself, the former Dewanohana Kuniichi. His first bout was in July 1963, aged just 15. At first fighting under his real name, he took on the "shikona" of Mienoumi in July 1966, but did not adopt the Tsuyoshi given name until September 1976. After being personally trained by the new Dewanoumi Oyakaya, former "yokozuna" Sadanoyama, he developed his technique and was promoted to the "jūryō" division in March 1969, and "makuuchi", the top division, in September 1969. In July of the following year, he reached the rank of "komusubi", defeating two "yokozuna" (Taihō and Tamanoumi) and receiving his first prize for Outstanding Performance. He was promoted to "sekiwake" in the next tournament in September 1970.