In a certain town lives a humble middle-aged adventurer, "Ojisan," who takes on quests from the guild. However, his true identity is that of a dungeon monster, a "Shape Shifter." Using his special ability to transform, he decided to live a carefree second life in a peaceful human town. He even befriends Alisa, the guild's receptionist, and seems to have achieved the life he'd always wanted. But his inherently good-natured nature leads him to get carried away by his emotions and end up getting involved in all sorts of troubles. However, each time, Ojisan uses his transformation skills and the experience and wisdom he's cultivated in the "monster world" to solve the incidents one after another.