Scouted by Jinsei Shinzaki, Yuasa trained at the Michinoku Pro Wrestling dojo and debuted in the promotion in 1999.

Despite the loss, Yuasa impressed the pundits so much that he was invited to the Young Lions Cup tournament in NJPW, reaching the finals and facing Ryusuke Taguchi in a losing effort.

At the end of the year, back in Michinoku Pro, Yuasa adopted the name of Gaina and the gimmick of a rock star, dying his hair green and becoming more aggressive and cocky.

His involvement with M-Pro had not ended, as he competed again for them during a interpromotional feud, beating Michinoku's Takeshi Minamino with the aid of the referee Ted Tanabe, and eventually capturing the Tohoku Junior Heavyweight Championship from Great Sasuke.

Similarly, Osaka Pro would receive back their tag team title from Rasse and Kagetora, thanks to Gaina and Zero.