After Koutarou Satomi's father is suddenly relocated for his job, the first-year high school student is faced with finding a cheap place to live by himself. Naturally, he jumps at the chance to move into Corona House's Room 106 for a mere five thousand yen a month. But while everything goes well at first, Koutarou soon gets a lot more than he bargained for after stumbling upon a mysterious cave while working his part-time job.

The following night, Koutarou is visited by various seemingly mythical figures, all of whom claim ownership of the poor student's apartment. Among the invaders are Sanae Higashihongan, a ghost supposedly haunting the room, magical girl Yurika, alien princess Theiamillis Gre Fortorthe, and Kiriha Kurano, a direct descendant of the Earth People. But more importantly, each of these four girls needs Koutarou's apartment for her own reasons and won’t back down without a fight!

Rokujouma no Shinryakusha!? is a comedic battle royale over a six-tatami mat apartment involving supernatural beings, romantic high school hijinks, and a deceptively cordial landlady.