After graduating and moving to Tokyo, he started training mixed martial arts at Satoru Sayama's Super Tiger Gym and eventually became an instructor.
When he arrived in Canada, he joined Stu Hart's Stampede Wrestling in Calgary, where he used the ring name Sumo Hara.
In December 1990, Kitahara took part in the original four-man tournament for the SWS Light Heavyweight Championship, but lost to Naoki Sano in the semi-finals when a doctor called a stop to the match.
After WAR folded, Kitahara focused primarily on Capture International, while taking select shows and tours of various promotions, including a brief return to AJPW in 2001, where he won the All Asia Tag Team Championship with Arashi, and also with Tenryu Project.
On April 2, 2018, Kitahara announced his retirement to take place at a June 11 card promoted by AJPW dojo classmate Kenta Kobashi, which will also be his 30th anniversary.
In a tag team match, Kitahara and Mitsuya Nagai lost to Naomichi Marufuji and Super Tiger II.