Demon Diary [Manga]

“Demon Diary is a light story about Raenef, a newly appointed Demon Lord, and Eclipse, his instructor, who is both a powerful demon and a veteran of a human-versus-demon war. Because of his actions during the Hangma War (which are not elaborated upon), he became known for his cruelty and incredible power. However, when attempting to teach Raenef, Eclipse’s ‘anger’ is often played for laughs.” [Wikipedia]