Kazuya Yuasa is a Japanese professional wrestler, better known for his ring names Gaina and Shisao. He has worked in Michinoku Pro Wrestling, Osaka Pro Wrestling and Okinawa Pro Wrestling, having titles in all the three promotions.

Michinoku Pro Wrestling is a Japanese professional wrestling promotion founded by The Great Sasuke on October 1, 1992. It was the first independent wrestling promotion in Japan to not base its operations in Tokyo, but rather in Morioka, Iwate. Since the promotion is primarily focused on the Lucha libre style of wrestling, many of their wrestlers don masks and special motifs as they compete in the ring. However, Michinoku Pro has accepted wrestlers from various styles and backgrounds over the years. In 2003, Sasuke left the running of the promotion to Jinsei Shinzaki.