Twenty-six-year-old Mamoru Hitomi, known on social media as the Angel of HR, is in reality a fraud: a luckless-faced consultant with no field experience who serves only as her company's glamorous poster girl. Frustrated with her hollow role, she drowns her sorrows at a bar one night, looking so plain in her bare face that no one recognizes her. There she meets Shiori Sakyo, the handsome, iron-fisted president of the small apparel maker Jet Black. He sees through her disguise, blackmails her with a photo of them sleeping together, and forces her to accept a consulting contract for his company. Jet Black is a textbook black company—new employees have a one-hundred-percent turnover rate, and the office is terrorized by a clique of monstrous employees known as the Mount Four Heavenly Kings. Hitomi, desperate to become a true consultant, throws herself into the mission.

The four Kings each embody a different toxic trait. The first is Erika Koenji, a hot-tempered accounting veteran who belittles subordinates and flies into rages. Hitomi defuses her not by punishment but by redirecting her passion into constructive channels. Next is Arisa Momoi, a sales ace and Sakyo's secret admirer. Jealous of Hitomi's closeness with the president, Momoi orchestrates workplace sabotage and attempts to isolate her, but Hitomi wins her over by proving her own competence during a critical exhibition. The third is Maiko Tokiwa, a seemingly meek production manager who is in fact a cold manipulator. Hitomi and Sakyo gather evidence of her past schemes and confront her, breaking her hold over the office. The last and most dangerous King is Rei Misumi, called Sumeragi, a beautiful, genderless head designer who charms everyone and habitually seduces colleagues, wrecking relationships with no remorse. When Sumeragi threatens to leave and take half the staff with him, Hitomi and Sakyo stage a desperate counter-reform to keep the company together.

As Hitomi works through each crisis, her relationship with Sakyo deepens from wary alliance to mutual affection, though both suppress their feelings because a romantic entanglement could compromise her consulting role. Complicating matters further, the arrival of a new hire—Hitomi's narcissistic ex-boyfriend Hayami—threatens to destabilize both the office and her personal life. Hayami lies, exaggerates his achievements, and tries to seduce Hitomi again, but Sakyo and Hitomi together expose and neutralize him. Just as the company seems on the verge of becoming a healthy workplace, a new antagonist emerges: Ruri, Sakyo's former right-hand woman, who now runs a rival firm called NC. She orchestrates a financial assault on Jet Black, aiming to destroy it. Hitomi goes undercover inside NC to reform it from within but suffers a crushing setback, losing confidence. Sakyo arrives to rally the remaining Jet Black staff, and together they stage a comprehensive comeback, merging with NC's remnants to save the company.

In the final arc, the newly merged Jet Black operates smoothly for six months. The office has become a true white company. Sakyo is ready to advance his relationship with Hitomi, but she presents one last challenge: her contract is ending. She must decide whether to remain as a consultant or leave. The series concludes with Hitomi choosing to stay—not as a consultant, but on her own terms. Sakyo proposes, and the two build a life together. An epilogue shows them married with a daughter, and Hitomi visiting her late father's grave, having fulfilled his ideal of being a manager who lifts up people's efforts.