Yama Juugo is a high school boy who has moved to Nanae Island, also known as the Special Student Zone, after being kicked out of the house by his father. He has chosen to begin his solo life in room 202 of the Happy House, a one-room apartment plus kitchen with separate bath and toilet, including furniture, appliances, and extras for 5,000 yen per month. But when he enters the room, he sees a girl relaxing inside, watching TV...

After clearing the ruins in the classroom, Juugo, Tensai, and Daruku become members of the Adventure Club. At club president Yuiga Isshin's request, Juugo undergoes a trial administered by Nanana to get her to share the location of the next treasure. This complete, the Adventure Club sets off to the Rising Building. As they search for the ruins, Tensai quickly finds a certain door...