Kengo Mashimo
On August 16, 2003, Gentaro made his debut for Kaientai Dojo, teaming with Hi69 to defeat Kengo Mashimo and Kunio Toshima in a tag team match. During the following months, Gentaro formed a regular trio with Hi69 and Kazma. In December 2003, Gentaro, Daigoro Kashiwa, Hi69, Kazma, Psycho and Teppei Ishizaka made it to the finals of the Survivor-K tournament, before being defeated by Kengo Mashimo, Kunio Toshima, Mike Lee Jr., Miyawaki, Super-X and Yuu Yamagata. On July 3, 2004, Gentaro won his first championship in Kaientai Dojo, when he teamed with Yoshiya to defeat Daigoro Kashiwa and Teppei Ishizaka for the UWA/UWF Intercontinental Tag Team Championship. After a four-month reign, Gentaro and Yoshiya lost the title to Taka Michinoku and Ryota Chikuzen on October 30. Gentaro became a champion again on February 12, 2005, when he defeated Onryo for the UWA World Middleweight Championship. However, his reign ended just seven days later, when he was defeated by Boso Boy Raito. Afterwards, Gentaro took a four-month break from Kaientai Dojo to concentrate on his work in Apache Pro-Wrestling Army, defeating Psycho in his return match on June 11. The following month, he entered the Strongest-K tournament, defeating female wrestler Tomoka Nakagawa and Kunio Toshima to advance to the semifinals of the tournament, where, on August 6, he was defeated by Psycho. During the next four years, Gentaro only made three more appearances for Kaientai Dojo.