Jigoro Kuwajima

Shihan is the alias of the man who trained Agatsuma Zenitsu and Kaigaku. He was formerly a Pillar in the Demon Killing Corps.

Appearance
Shihan mainly appears in the manga through the forms of flashbacks, he can be physically described as a short, elderly man with silver or grey colored hair and a visible scar located below his left eye. He is commonly seen in the manga wearing a jinbei styled kimono similar to the one worn by Sakonji Urokodai.

History
Shihan was the instructor of Zenitsu and Kaigaku as the former Thunder Pillar. He favored Kaigaku over Zenitsu as his Successor since Kaigaku manages to master most of the Thunder Breath Styles, except the First Step. While Zenitsu only manages to master only the First Step due of his inexperience.

He committed suicide by seppuku when his former protege defected to gain the powers of a demon. Shihan death was slow and agonizing since no one could cut his head while he commits suicide. His death ultimately making Zenitsu as the next Thunder Pillar, as well becoming Zenitsu motivation to kill Kaigaku.

After Zenitsu manages to kill Kaigaku, Zenitsu and Shihan briefly meet in the afterlife, with Zenitsu apologizing to his master, since in the end, they couldn't get along. Before Zenitsu forcefully returns to the land of living, Shihan declares that Zenitsu is his Pride and Joy in tears.

Quotes

 * (To Agatsuma Zenitsu) "Zenitsu, go the distance. You can run, you can cry, but don't give up. I believe in you. You've endured a hellish training regimen every single day. You will definitely be rewarded. Strike until it's at its limit! Become a blade! That is stronger than anyone else!!"