He first tried sumo in the third grade when he entered a competition for fourth graders and up and came in third. By middle school he was training every day at a sumo dojo. He met Takahanada (later the 64th yokozuna Takanohana) when a regional tour came to Hirozaki City, getting into the ring with him. He entered professional sumo in March 1992 after completing middle school, although he had been admitted to Hirosaki Jitsygyo High School. He had received offers from four or five different heya upon his graduation, but the small and relatively new Naruto stable appealed to him.
As with many sumo wrestlers, he initially competed under his family name, Kogawa, but upon reaching the second highest jūryō division in November 1997 he was given the fighting name of Wakanosato, reminiscent of his stablemaster, former yokozuna Takanosato.
He entered the top makuuchi division for the first time in May 1998. He was holding his own that year and even recorded his first kinboshi or gold star win against yokozuna Wakanohana, but the very next day he broke his ankle in a match with Musōyama and had to miss the last day of the tournament and all of the following tournament. He suffered a more serious injury in November 1999, rupturing anterior cruciate ligaments. He sat out two successive tournaments after having surgery and was demoted to the jūryō division . He won consecutive jūryō championships upon his comeback, in May and July 2000, and was promoted back to makuuchi in September. He quickly made the titled san'yaku ranks, making komusubi in November 2000 and recovering from 2–6 down to finish 9–6. As a result, he was promoted to sekiwake for the first time in January 2001.
In his early top division career, Wakanosato was considered a promising candidate for ōzeki. From January 2002 until January 2005 he spent 19 consecutive tournaments ranked at either komusubi or sekiwake, an all-time record. However, he was never able to break through the "great barrier" (the literal meaning of ōzeki), just failing to attain the necessary 33 wins over three tournaments. He was runner-up in the January 2003 tournament, and again in September 2003, where his 11–4 score was probably his best chance to make ōzeki. However, he could only manage seven wins in the following tournament. He was never able to consistently beat the top ranked wrestlers, being unable to beat Takanohana in nine attempts and winning only five times out of 32 meetings against ōzeki Chiyotaikai. Nevertheless, he was awarded ten sanshō or special prizes for good performances in tournaments during his career.
In later years on the dohyō he again had injury problems, being forced to withdraw from his final san'yaku-ranked tournament in September 2005 and missing all of the next. He defeated yokozuna Asashōryū on the second day of the 2006 May tournament, his first kinboshi in 45 tournaments (only Kirinji, with 47 tournaments, has had a longer wait between kinboshi) but he could only manage a 6–9 record overall. He was then again forced to sit out all of the September 2006 tournament and fell to the second division once again. However, he made something of a comeback in May 2007, turning in a strong 10–5 record at maegashira 7. He won his 600th career bout in September 2007, and turned in another good performance in May 2008, again finishing on 10–5.
He withdrew from the March 2009 tournament after breaking a metatarsal bone in his right foot during his 11th day bout with Kotoshōgiku. He had surgery on 8 April which put him out of action for at least two months, meaning he had to sit out the following tournament in May. He came back very strongly in July, winning his fourth jūryō championship with a 14–1 record. He reached maegashira 1 in March 2010, his highest rank in over four years. After that he comfortably maintained a position in the mid-to-upper maegashira ranks until he was injured in the November 2011 tournament, resulting in yet another fall to jūryō. However he immediately returned to makuuchi after scoring 11–4 in January 2012.
After a poor 4–11 record at maegashira 15 in September 2013, Wakanosato was once again demoted to jūryō, but for the first time for a non injury-related reason. He was ranked in makuuchi only one more time after that, in the July 2014 tournament.
Following a 4–11 result in jūryō in July 2015 which guaranteed a further relegation, Wakanosato announced his retirement on 3 September. He told a press conference "I entered this career out of my love for sumo, and it has been enjoyable. I'm being sincere in saying I want to continue, but my body is not up to the task of matching my desire." He has purchased a toshiyori-kabu or elder stock in the Japan Sumo Association and is now known as Nishiiwa Oyakata. He is working as a coach at his old stable, now renamed Tagonoura following the death of his stablemaster. His official retirement ceremony or danpatsu-shiki was held at the Ryōgoku Kokugikan on 28 May 2016.
Wakanosato specialised in yotsu-sumo, or techniques that involve grabbing hold of the opponent's mawashi. He was known as being particularly difficult to beat once he has got a migi-yotsu, or right hand inside, left hand outside grip. About 40 percent of his wins are by yori kiri, or force out, but he was also good at pushing and thrusting, winning many bouts by oshi-dashi or push out. His two most commonly used throws were sukuinage (scoop throw) and uwatenage (overarm throw).
Wakanosato initially had an excellent head-to-head record against Hakuhō, defeating him the first six times they met. However, the last of these victories came in 2005 and he subsequently lost eleven in a row against him.
Wakanosato was married in April 2004. His stablemaster reported that his bride weighed just 39 kg (86 lb; 6.1 st).