Confident and picky gay professional Kaji initially dismisses his gloomy colleague, Fukami, as completely unattractive. However, a shared hotel room during a business trip reveals Fukami's hidden beauty, leading to an intense overnight encounter. While Kaji assumes he has won Fukami over, he is left stunned when the reserved technician coldly rejects him the following morning.
After failing to find a suitable partner on dating apps, Zero decides to pursue a second encounter with Fukami. Following an intimate session, the two agree to enter a casual sexual relationship, provided they adhere to one strict rule: neither of them is allowed to fall in love.
After mistakenly believing Fukami is engaged, the protagonist visits his home and discovers his selfless devotion to his siblings. Seeing a more human side of the usually distant Fukami shakes her perception of him, and as his passionate nature during their intimate moments contrasts with his cold exterior, she finds herself fighting an unexpected attraction.
Seeking to discover if Fukami's charm persists when he loses control, the female lead invites him for drinks as a social experiment. After a night of intense passion at his place, she finds herself captivated by his assertive drunk persona, only to be shocked the next morning when he has no memory of the encounter.
Conflicted by a growing obsession, the protagonist attempts to seize dominance in their sexual relationship to avoid falling in love. However, they quickly find themselves submitting once again, leaving them frustrated by their inability to resist their partner's allure despite viewing him as unremarkable.
Following a moment of unexpected tenderness, Fukami's relationship with Kaji is thrown into turmoil when he discovers he has been labeled as "40%" in Kaji's address book. A confrontation with another of Kaji's partners exposes the cold way Kaji ranks his lovers, leading to a painful fallout and a sudden breakup.
Kaji reflects on his detached view of romance before sharing an intimate encounter with Fukami, where he finds himself unexpectedly attracted to the other man's strength. However, this moment of connection is abruptly shattered when Fukami is rushed to the ICU after suffering a sudden cardiac arrest.
After a bicycle accident lands Fukami in the hospital, he confesses his love for Kaji and expresses a desire to move beyond their casual arrangement. While Kaji admits his strong physical attraction, he struggles with the idea of romance, leading the pair to agree to remain friends with benefits for the time being.