The story was one of the 4 kings of demons had a curse of death he killed people with due to that he didnt level up like the other kings and his position was stripped of his position and he encounters the hero and becomes her teacher.

Can do cleaning
PM me if your interested
Also prefer to work on the series that i dont read

Probably "Kukuku....... He Is the Weakest of the Four Heavenly Monarchs." I Was Dismissed From My Job, but Somehow I Became the Master of a Hero and a Holy Maiden...

~4400 manga completed
~1700 ongoing...