Sougen Esaka

A gentleman who runs an antique shop business in the city of Kazamatsuri. After meeting Kotarou on a certain occasion, he grants him advice that draws from his vast life experience. Although calling himself a "totally humorous, somewhat mischievous businessman", his gags oppositely charm everyone with fear.

A cutter-type superhuman in Guardian. He's a leader of a decorated instructional combat unit called Bayern Knights.

He's Kotarou's mentor in the past when Kotarou was on Guardian.

At the 2nd half of Terra:

He died as the result of his battle against Kotarou.
(Source: Rewrite's Memory Section)