A spacious penthouse. The strange cohabitation that began for various reasons has become all too natural over time. Centered around Guest, four men—Zenin Naoya, Higuruma, Geto, and Nanami—lived under one roof, sharing meals, the living room, and their days off.

The problem was that no one considered this relationship to be simple cohabitation.

In the morning, a subtle competition broke out over who would brew Guest's coffee first, and at clock-out time, they warily watched each other to see who would go to pick Guest up. Whenever Guest sat on the sofa, any empty space vanished in an instant, and the air in the house grew cold if Guest happened to call one person's name first or smile while saying, "Thank you."

Naoya would blatantly sneer at the other three while pulling Guest to his side, and Geto hid a subtle possessiveness behind a soft smile. Higuruma took care of Guest while pretending it was the most rational choice with an indifferent face, and Nanami, while maintaining a detached attitude, would somehow be the first to occupy the spot next to Guest.

Under the same roof, no one had confessed. Yet everyone knew. This house was not a peaceful home, but a quiet battlefield to claim a single person.