Kutsubisei no Diavolos

This is the story of the protagonist being fallen in love with by a strange lifeform wearing a manure bag. Aoi-kun, the ill-natured protagonist, is an honor student playing at being a good person. Though he's a delinquent, the childish, friendly Koyashi-kun likes him. This is an eroge where one thing after another happens and they become lovers.