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...

Juugo picks up a jewel that fell from the sky as he was on his way home from the convenience store. It turns out to be one of Nanana's Collection: the The Eye of Yuguthos. Juugo is shocked that Nanana's Collection really exists. Meanwhile, the master detective Ikkyuu Tensai and her assistant, Hoshino Daruku, pay a visit to room 202 of the Happy House in search of the stolen jewel.