Otsuka became one of the greatest Battlarts stars, feuding with Daisuke Ikeda and Yuki Ishikawa in violent matches and brawls, and being also part of the Love Warriors tag team along with Mohammed Yone.
In 2006, Otsuka started competing in Michinoku Pro Wrestling under the gimmick of Otoko Sakari (男盛), a bisexual, sex addict wrestler who wore a fundoshi and utilized sexual antics against his opponents.
Sakari never took off as a serious contender, as he often lost matches by morodashi (モロダシ, being exposed in public) when his opponent compromised his attire, making the ring crew throw the towel to cover it.
Going against the pundits' judgement, Otsuka showed his skill and tenacity when he managed to take Ruas down and perform ground and pound through his guard, as well as later defending a fully locked rear naked choke to the end of the round.
It was later revealed that Ruas fought under medication for hepatitis and a knee injury,[3] but nonetheless the Japanese press lauded it as one of the biggest upsets ever, and Otsuka won the Tokyo Sports magazine topic award for his victory.
Renzo executed a German suplex-like takedown and tried an arm triangle choke, but Alexander was never inactive and even threatened with a Kimura lock before the match ended, with a unanimous decision for Gracie.
After losing two fights against Guy Mezger, Otsuka was put against Pride middleweight champion Wanderlei Silva, who had defeated many Japanese names in his way, including Kazushi Sakuraba and Daijiro Matsui.
He survived for two rounds, absorbing punches, knees and soccer kicks in his attempts to get the takedown, which he accomplished, gaining north/south position at the end of the second time, though he couldn't capitalize on it.
The fight was a heated one, with Alexander being cornered by Mexican wrestler Solar, who had been disqualified weeks before by hitting Minoru Suzuki with a low blow in his MMA debut.
Alexander continued dominating, hitting hammerfists to the head and even locking a crucifix, but the injury was too grave to keep on and Yamamoto came back with his own knees, making Otsuka throw the fight.
The restarted fight was fast, with Otsuka absorbing knee strikes and attempting heel hooks until Murilo got an arm triangle choke, making him tap out.