He won the fight by a first-round knockout, stopping Fujimasa with a spinning backfist near the end of the opening round.
[6] Otsuki challenged the reigning WPKC World muay thai champion Satoshi Kobayashi at AJKF Survivor on January 4, 2005.
[9] Otsuki next faced Jon Sung Min at AJKF New Year Kick Festival 2007 on January 4, 2007.
[10] Otsuki's two-fight winning streak was snapped by Hiromasa Masuda at AJKF: Departure Norainu FINAL on March 9, 2007, who beat him by unanimous decision.
[11] Otsuki suffered his second consecutive loss on June 17, 2007, as Kupee Wor.Steera beat him by unanimous decision at AJKF's Thailand event.
Otsuki was booked to face Kanongsuk Weerasakreck in the quarterfinal bout of the AJKF 60 kg tournament, which was held on August 25, 2007.
[15] After winning his promotional debut, Otsuki was scheduled to participate in the 2009 Krush lightweight grand prix.
Although he beat Hiroshi Iwakiri by a first-round technical knockout in the opening round of the tournament, he lost a majority decision to Masahiro Yamamoto in the quarterfinals, which were held on the same day.
[19] Otsuki returned from a three-year absence from the sport to face Taishi Hiratsuka at Krush 34 on November 10, 2013.
[22] Otsuki extended his winning streak to three straight fights at Krush 37 on April 1, 2014, as he beat Junpei Aotsu by split decision, after an extra round was contested.
He won the fight by a first-round stoppage, as Damashii's corner threw in the towel at the 1:36 minute mark.
[31] Six months later, at SIAM WARRIORS SUPERFIGHTS on October 22, 2016, Otsuki won the ISKA Muay Thai Intercontinental Super Lightweight title with a first-round knockout of Saen Kransi.
Otsuki was next booked to face Starboy Kwaythong Gym at the inaugural KNOCK OUT event on December 5, 2016.
He first lost to Yuto Tsujide by a first-round knockout at HOOST CUP KINGS KYOTO 2 on March 5, 2017.
[34] Two months later, at KNOCK OUT 2017 in Ryogoku on December 10, 2017, Otsuki suffered a third-round stoppage loss to Hikaru Machida.
[37] Otsuki faced the Shootboxing Japan lightweight champion Renta Nishioka at SHOOT BOXING S-cup 65 kg World TOURNAMENT 2018 on November 16, 2018.