He is best known for his time in Pro Wrestling Noah, however he started his career in All Japan Pro Wrestling (AJPW), before moving to Pro Wrestling Noah; through Noah's involvement in the Global Professional Wrestling Alliance, a global organization of cooperative promotions that allow their competitors to travel abroad to other companies, he has wrestled extensively in American promotion Ring of Honor (ROH). He initially wrestled under his real name, but due to potential confusion with his mentor Kenta Kobashi (in both English and Japanese), he dropped his surname and began only using his given name, which he spells with Roman letters in all capitals.
Kobayashi has won several professional wrestling championships in his career: he is a former one-time Global Honored Crown (GHC) Heavyweight Champion, three-time GHC Junior Heavyweight Champion, three times GHC Junior Heavyweight Tag Team Champion, and one-time GHC Tag Team Champion; once was the inaugural reign with longtime partner and rival, Naomichi Marufuji, which saw the two hold the title for almost two years, as well as a reign with protégé Taiji Ishimori. He was also the winner of the 2012 Global League and the 2013 Global Tag League tournaments.
- Global Honored Crown Heavyweight Championship
- Global Honored Crown Junior Heavyweight Championship
- Global Honored Crown Junior Heavyweight Tag Team Championship
- Global Honored Crown Tag Team Championship