Morishima debuted for All Japan in 1998, but left in 2000 to join the newly formed Pro Wrestling Noah (founded by Misawa), where he became a mainstay.

[5] On March 2, 2008, Morishima defeated Mitsuharu Misawa at the Budokan Hall Event of Pro Wrestling Noah's Second Navigation Tour to become the 12th GHC Heavyweight Champion.

On September 6, 2008 at the Tokyo Nippon Budokan, Morishima lost to Kensuke Sasaki, who gained a pin at the 22-minute mark with the Northern Lights Bomb.

[8] Since this victory, Morishima has defended against Naomichi Marufuji, Maybach Taniguchi, Go Shiozaki, Akitoshi Saito, Kenta, Jun Akiyama, and Kohei Sato.

[10] Post-match, Morishima quit Brave to form a new group with Kenoh and Maybach Taniguchi, later named Choukibou-gun,[11] turning heel in the process.

[12] On January 25, Morishima and Taniguchi defeated TMDK (Mikey Nicholls and Shane Haste), with help from Kenoh and new stablemate Hajime Ohara, to win the GHC Tag Team Championship.

He lost to Samoa Joe on February 16, 2007 before defeating Homicide in a match for the ROH World Championship on the subsequent evening, thus becoming the first non-American to hold the title.

[18][19] Back in ROH, Morishima went on a string of successful title defenses, defeating the likes of Austin Aries, Shingo, Jay Briscoe, and Roderick Strong.

[6] On July 16, 2007, Morishima wrestled in the main event of Ring of Honor's debut show in Japan and defeated Nigel McGuinness to retain the ROH Championship.

On April 21, Noah announced that a blood test had revealed that Morishima had an abnormally high glycated hemoglobin, suggesting diabetes.

[26][27] The show, initially named Genesis, was scheduled to take place on October 15, but was cancelled after Morishima announced he required emergency surgery for arthritis in his foot.