Yuuki Shinji is a 35-year-old single salaryman living with his parents, with no romantic experience and a growing anxiety about spending the rest of his life alone. A chance incident on a shinkansen changes everything: an elderly man suffers a medical emergency, and Shinji calls for help, drawing together a group of six strangers—a doctor, a former nurse, and others—who cooperate to save the man. The grateful millionaire rewards them by offering the use of a luxury penthouse apartment as a shared residence. Shinji, along with five other adults of roughly the same age, moves into the extravagant tower apartment, where the housemates agree on a rule that no romantic relationships are allowed among residents.

Among the new housemates is the doctor who treated the elderly man, Ban Eriko. She is accomplished and attractive but also romantically inexperienced and carries trauma from a past relationship. Unaware of Shinji’s feelings, Eriko proposes a “love training” arrangement—a simulated relationship in which the two can practice dating and romance in a low-pressure way, with the goal of overcoming their mutual awkwardness. Shinji agrees, and they begin a series of practice dates, everyday interactions, and shared moments that gradually blur the line between pretense and genuine affection.

As Shinji realizes he is sincerely falling for Eriko, their fake relationship deepens into real emotion. Their progress is complicated by the arrival of a new housemate, Asai Harutaka, Eriko’s ex-boyfriend who originally caused her romantic trauma. His presence reopens old wounds and creates a love triangle, with tensions flaring during a night pool date and other group activities. Despite the challenges, Shinji and Eriko eventually confess their true feelings and become actual lovers, though they keep their relationship secret from the other housemates.

The story follows their relationship as they navigate typical hurdles of adult romance: misunderstandings, a first trip together, meeting family members such as Eriko’s older brother, and dealing with the troubles of fellow housemates—particularly Fukami, a divorced resident whose ex-husband causes problems. A new resident, the wealthy and sheltered Rin, brings additional chaos and inadvertently spurs romantic developments among other housemate pairings. Later, the couple faces more serious obstacles as Eriko becomes physically and mentally exhausted from work and personal stress, and the landlord issues an unexpected eviction notice threatening to dissolve the shared house. Shinji and Eriko must confront whether their relationship can survive real-world pressures and whether they can build a future together.

Throughout the story, the setting of the luxury tower apartment remains a backdrop for the interactions of an eclectic group of adults learning to handle love, friendship, and life in their thirties. The narrative follows an overarching trajectory from awkward romance training to genuine commitment, interwoven with the evolving relationships of the supporting housemates.