He captured the tournament title with three consecutive unanimous decisions in a single day, as he was able to overcome Kosuke Minowa in the quarterfinals, Taishi Hiratsuka in the semifinals and Yusuke Tsuboi in the finals.
Kusakabe beat Ryuma Tobe by unanimous decision in the opening round and future two-weight Krush champion Daizo Sasaki by a first-round knockout in the quarterfinals.
He advanced the to tournament semifinals, held on December 31, 2008, where he suffered a third-round technical knockout stoppage at the hands of the future two-weight K-1 champion Koya Urabe.
[10] He won the fight by a third-round technical knockout and advanced to the Ceasers Cup final, held on the same day, where he faced Kazuyuki Fushimi, who he had beaten by unanimous decision two years prior.
[11] The tournament victory earned Kusakabe the right to challenge Phantom Shinya for the Shootboxing Japan Super Bantamweight Championship at "Anniversary Series 4 -ISHIN- So no Yon" on September 18, 2010.
He won the fight by unanimous decision and advanced to the final, held on the same day, where he faced Shota Takiya for the inaugural Krush Super Bantamweight title.
[20] Kusakabe made his first WBC Muay Thai Japan Super Bantamweight title defense against Keisuke Miyamoto at NJKF KICK TO THE FUTURE 6 on September 22, 2012.
After he successfully bounced back from his second professional loss at the hands of Miyamoto, Kusakabe made his first WPMF Japan Super Bantamweight title defense against Sota Ichinohe at HOOST CUP KINGS Oujatachi no Kyouen on June 16, 2013.