Learned from Demonologist in the underground city after completing Demon Worshipper 101. Requires MATK ≥ 40 and MP ≥ 200. Learning the spell takes three full days.
Acedia is a very powerful spell hitting all enemies. It is however highly impractical because of its very high MP cost. Only specific builds focusing on a high MP pool will get to benefit from Acedia. Learning this spell is still a way to earn some Trust in the underground city. So just learning this spell without can be useful.