Sota Yukimura (Hokuto Matsumura) works in the secondary brand division of the cosmetics company "Nose Cosmetics." For 25 years, he has harbored an unwavering, unrequited love for his boss—and first love—Mariko Nose (Sae Okazaki). Sota, who would brave any danger for Mariko's happiness and constantly rescues her from trouble from the shadows, suddenly finds himself a murder suspect. Just before Tsuyoshi Tateiwa (Tomomi Maruyama)—an executive who had been at odds with Mariko—was killed, security camera footage near the scene captured Sota's image. Questioned by Detective Taisuke Sakura (Tetsuji Tamayama) of the First Investigation Division, Sota admits to meeting Tateiwa shortly before the incident but denies the murder... Meanwhile, completely unaware that suspicion has fallen upon him, Mariko feels gloomy as her birthday approaches. It is a Nose family tradition to hold a gathering at the family home every year for her birthday, yet Mariko detests these parties... She adamantly refuses to communicate with her father—company president Ginjiro Nose (Ken Ishiguro)—about anything other than work. What exactly is the root cause of this rift? Wanting to see Mariko smile, Sota concocts a work-related excuse to visit the Nose residence, attempting to infiltrate the birthday party to discover why she dislikes the occasion... What dark secrets of the Nose family await him?

"Just what are you to Mariko?" Sota Yukimura (Hokuto Matsumura), an employee in the secondary brand division of "Nose Cosmetics," is summoned by Sayuri (Miki Mizuno)—the stepmother of his boss and unrequited love, Mariko Nose (Sae Okazaki)—and grilled about his relationship with her. Sayuri has thoroughly investigated Sota's background; he is the same age as Mariko and has followed the exact same path—junior high, high school, university, and even the same company—for twenty-five years. Intent on ousting Mariko—who stands in the way of her own biological son, Keito (Junsei Ishiyama), inheriting the company—Sayuri uses a secret of Sota's as leverage to make a specific demand... Meanwhile, Mariko begins to wonder if the boy who saved her at a summer festival during her junior high years was actually Sota. However, upon learning that he has feelings for another woman, she decides to rule him out as a potential romantic partner. Her secretary, Izumi Takeda (Nozomi Sasaki)—who often struggles with Mariko's obliviousness—appeals to her true feelings, asking, "Why take him off the list? What about your own heart?"... Amidst this, Mariko's father and the president of Nose Cosmetics, Ginjiro Nose (Ken Ishiguro), is baffled when he loses contact with his secretary, Gota Asai (Atom Shukugawa), who had suddenly taken leave. Suspecting the involvement of Satoru Hatano (Yoji Tanaka)—a serial kidnapper recently released from prison—he begins searching for Asai's whereabouts... Furthermore, Taisuke Sakura (Tetsuji Tamayama), a detective from the First Investigation Division who views Sota as a suspect in the Tateiwa murder case, obtains new information regarding the incident... As their various agendas swirl together, Sota's love life takes a dramatic turn!