Listless geek Mizuto Irido and introverted nerd Yume Ayai seemed like a match made in heaven, connected by their mutual love for literature. Unfortunately, their differences gradually grew, and they separated just after their middle school graduation. But, as if by divine comedy, the two find themselves reunited as step-siblings. A rivalry begins to brew between the former couple, both unwilling to acknowledge the other as the older sibling. In an attempt to solve this issue, Mizuto and Yume agree upon a rule: whoever crosses the boundaries of siblinghood norms loses, and the winner will not only be called the older sibling, but also get to make a request. However, now that they live under the same roof, the lingering memories they share start to influence their actions—possibly rekindling the feelings that may not have been fully extinguished in the first place.

Keitaro Urashima promised a girl when he was young that they would meet up again at Tokyo University in the future. Sadly, in the National Practice Exam, Keitaro ranked 27th from the bottom. Knowing his grandmother owned a hotel, Keitaro intended to stay there while continuing his studies for Tokyo U, only to find out the hotel had long been transformed into an all-girls dormitory. Through an odd twist of fate, Keitaro eventually became the manager of the dorm, beginning his life of living with five other girls.

Yuuki Aito is a perverted manga artist who appreciates panties, wishing to draw as many as he can. Being surrounded by numerous female assistants, he is constantly asking to use them as references for the manga he draws. Although Aito has an extremely degenerate mind, he can also be a very kind, generous, and helpful person. The duality of his behavior confuses his assistants—do they love the considerate side of him that he rarely displays, or do they hate him for the perverted thoughts he has most of the time?

Serial murders have recently plagued Inaba, with the police struggling to find any leads. Despite this, due to his parents going abroad for work, Yuu Narukami moves to the small town to live with his uncle for a year. He enrolls at Yasogami High School, where he meets and befriends Yousuke Hanamura, Chie Satonaka, and Yukiko Amagi. While hanging out together after school, the group fills Yuu in on the urban legend known as the Midnight Channel—a mysterious TV channel that only appears at midnight on rainy days while the viewer is alone. Curious about the claim, Yuu decides to tune in that night, only to see the next victim of the serial murders appear on the screen instead. He also finds himself being drawn into the TV, which intrigues his newfound friends enough to want to investigate. Yuu ends up falling into the world within the TV, which is blanketed by a thick fog and swarming with hostile creatures known as Shadows. Realizing that this world is somehow connected to the murders, the Investigation Team forms with the goal of uncovering the mystery behind the incidents.