Monsters are coming to the human world from the Hell in order to get human spirits. As people's minds are getting dirty, being attracted by the dirty spirits, the monsters break the rule to go to the human world.

Tsutomu, a boy who goes to Yokai Elementary School, is suddenly assaulted by monsters. Those who save him from the monsters are Enma-kun, the son of Enma, Yukiko, a snow woman, and Kapaeru. They are members of Monster Patrol that are sent to the human world to arrest monsters.

(Source: AnimeNfo)