Two years have passed since the conclusion of the battle with the formidable foe known as Rumour. Akira Sato, the legendary hitman codenamed Fable, continues to live a quiet life with his associate Yoko and his neighbor Misaki, striving to maintain the ordinary existence his boss ordered him to adopt. The third part of the series follows Akira as he persists in his endeavor to lead a normal life, though the peace is soon disrupted when a certain man arrives with a visit that threatens to pull him back into the dangerous underworld he left behind.

The story is set in the same world as the previous installments, a reality where professional killers and yakuza clans operate beneath the surface of Japanese society. Akira Sato, a soft-spoken young man with an unpredictable temperament, is in reality a genius assassin feared throughout the Japanese underworld. His signature weapon is an anthracite-colored Nighthawk pistol, and his skills are so refined that he can eliminate any target within six seconds. Yoko Sato, his partner, acts as his driver and assistant, possessing a photographic memory that makes her an invaluable ally. Misaki Shimizu, a woman living in the apartment next door, has become an important part of their daily lives after being pulled into Akira’s world during the previous story arcs.

The initial narrative arc of The Third Secret focuses on the return of complications from the past. Following the departure of the killers Azami and Yukari from Taihei City, Akira and Misaki had settled into a routine. However, the arrival of a mysterious man signals the beginning of a new conflict. This situation forces Akira to confront the fundamental contradiction of his existence: the struggle to adhere to his boss’s absolute rule against killing anyone, even as he is surrounded by criminals who could provoke him at any moment. For this human weapon, living as an ordinary citizen remains the most difficult contract he has ever taken, and this new development tests the limits of his no-kill policy in unexpected ways. The story also explores the emotional fallout and character development for Misaki, whose past and privacy become exploited behind her back, creating a tense situation that eventually sets the stage for a larger confrontation involving new adversaries such as a pair of hitman twins.