Demon King Daimao

Demon King Daimao is a light novel series that received an anime adaptation which aired in 2010.

Set in a time where magic has become commonplace, the story follows Akuto Sai, an orphaned teenager who transfers to the Constant Academy of Magical Arts in order to achieve his dream of becoming a High Priest. However, his dreams are dashed when the aptitude test he took upon arrival prophesies that he is destined to become a Demon Lord. As word spreads of this revelation, Akuto's school life becomes complicated as the school populace becomes to fear him, but he is determined to ensure that his future fate is not set in stone.

OP
Akuto is seen with his shirt unbuttoned.

Episode 3
Akuto and Hiroshi take a bath.