[3] He was one of the longest serving ōzeki in sumo history, holding the rank for 47 consecutive tournaments until November 2013.

In January 2014 Kotoōshū obtained Japanese citizenship, a requirement of becoming an elder in the Japan Sumo Association,[4] and he announced his retirement during the following tournament in March.

[7] He hoped to compete for Bulgaria in the 2000 Olympic Games, but as his weight increased beyond the 120 kg upper limit, he switched instead to sumo.

[8] He was recruited by Sadogatake stable, whose stablemaster was impressed by his filial duty of sending money home to his parents.

He was given the shikona of Kotoōshū, derived from his place of origin — koto, shared by all wrestlers at his stable, and ōshū, meaning Europe.

(Following the September 2006 tournament, he changed one of the characters in his ring name, 州 becoming 洲, although the pronunciation, shū, is the same for both.)

In the July 2005 tournament Kotoōshū defeated Asashōryū for the first time with an overarm (uwatenage) throw, bringing to an end a run of 24 consecutive bout victories for the yokozuna.

An 11–4 record in the final (November) tournament of 2005 was his third runner-up performance in a row and included another victory over the otherwise dominant Asashōryū.

Although he was not the youngest ōzeki ever, this represents the most rapid rise for a wrestler entering sumo from the bottom jonokuchi division.

He is also the first wrestler of European birth to hold the ōzeki rank, and the fifth non-Japanese to have achieved it (following Konishiki, Akebono, and Musashimaru from Hawaii and Asashōryū from Mongolia).

In October 2008 he denied allegations by disgraced former wrestler Wakanohō that he had thrown matches against Kotoōshū in return for money, saying "I am saddened by this.

[18] He returned in July and preserved his rank by securing his eighth win on Day 10 (the last bout of fellow ōzeki Kaiō's career), finishing on 9–6.

[19] In the May 2012 tournament Kotoōshū withdrew with an ankle ligament injury on the last day, handing opponent Tochiōzan his twelfth victory by default and eliminating Hakuhō and two maegashira from the yūshō race.

[25] He retired during the following tournament in March after 9 losses in a row, saying "I’ve had so many injuries recently, but I have no regrets because I gave it my utmost over 12 years.

Kotoōshū has remarked that his tournament victory was partially due to a weight gain of five kilos which enabled him to be sturdier against his opponents.

[36] One of the reasons that led to Kotoōshū's introduction to sumo wrestling was to help with the household, because his father could not work due to a traffic accident.

[40] They married in February 2010, on St. Valentine's Day, at the New Otani Hotel in Tokyo, with around 600 guests including yokozuna Hakuhō attending.

[42] He injured his right knee towards the end of the May 2010 tournament which required surgery and forced him to cancel plans to have a second wedding ceremony in Bulgaria, at the Evksinograd resort in Varna, during the European Sumo Championships.

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