Kotoōshū was promoted to "sekiwake" for the following September tournament and won his first twelve bouts, finishing with an exceptional 13–2 runner up record and only losing the tournament victory after a play-off bout with Asashōryū. 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. This led to his promotion to the rank of "ōzeki" on November 30, 2005. His three-tournament record (on which "ōzeki" promotions are based) was 36–9. His promotion coincided with the retirement of his stablemaster, former "yokozuna" Kotozakura.