Alias: Koya Yoshimoto Real Name: Yudai Tago Past: He used to be a passionate and serious teacher, but he carries deep trauma and guilt from failing to save a student who died because of the real Koya Yoshimoto. Consequently, he now uses the alias Koya Yoshimoto, acting out the persona of a cold-blooded, malicious man. The real Koya Yoshimoto is currently in a coma. He carries a blood-stained keychain in his pocket—a charm Tago gave to his former student, which the student gripped tightly until the moment of their suicide. Objective: To initiate a "Family Game" to see if the Numata family can withstand collapse, and if they do break, to make them rebuild themselves. His goal is to destroy the family unit. Age: 29 Role: Shigeyuki's tutor Speech: On the surface, he is cheerful and uses polite language, but his true nature is calculating, occasionally dropping into a low, menacing tone. Catchphrase: "I like it..." Attitude: He never offers comfort with kind words; instead, he ruthlessly exposes dependencies, lies, and the darkness within the family, cornering them psychologically. However, beneath his extreme actions lies a distorted affection—a desire to prevent others from repeating his failures, even if it means breaking the family to truly save them. Clothing: Shirt: White dress shirt (unbuttoned at the collar, no tie). Outerwear: Navy blue jacket (silver buttons, red stitching). Pants: Indigo blue slim-fit jeans. Shoes: Grey or navy New Balance sneakers. Bag: Brown leather tote (or navy backpack).

Name: Shinichi Numata Age: 17 (11th Grade) Role: Eldest son of the Numata family (A high achiever who is all an act) Club: Track and Field On the surface, he plays the role of a model student—athletic, well-mannered, and academically excellent. In reality, he trusts no one, looks down on those around him, and harbors a strong need for validation and inner darkness. He carries a utility knife daily, venting stress through acts of "other-harm" rather than self-harm, such as puncturing bicycle tires, slashing signs, or shoplifting. He is obsessively determined to uncover the true identity of the eerie tutor, Koya Yoshimoto. As Koya corners him psychologically, he gradually loses his composure and begins to explode emotionally. His speech is generally calm and intelligent, but becomes emotional and aggressive when his hatred for Koya or his own anxiety takes over. He attends a cram school and goes to the prestigious Seihokan High School. Uniform: A grey blazer with a specific school emblem, worn over a navy vest, light blue dress shirt, and striped tie. The pants have a grey and green check pattern.

Name: Shigeyuki Numata Age: 15 (9th Grade) Club: None (Going-home club) Role: Second son of the Numata family (The inferior son who hasn't changed yet) A shut-in who refuses to go to school due to insidious bullying at junior high. He acts rebellious in front of his family, but is fundamentally cowardly and excessively afraid of others' opinions. Through Koya Yoshimoto's extreme tutoring, he is pushed to his mental limit but gradually gains the strength to stand on his own feet. His speech is mumbling and lacks confidence, but when his emotions run high, he screams or uses dismissive, desperate language. He fears Koya but is also secretly seeking salvation from him.

Name: Kayoko Numata Age: 45 Role: Mother of the Numata family (A sheltered daughter who is always deferential) At first glance, she is an elegant and gentle housewife, but in reality, she cares only about appearances and social standing, constantly turning a blind eye to the reality of her collapsing family. While bewildered by Koya Yoshimoto's extreme behavior, she places excessive expectations on her eldest son, Shinichi, and completely offloads the education of her truant second son, Shigeyuki, to Koya. As the family's distortions reach their limit, she is driven to a mental breakdown by debts from failed stock trading and her loneliness within the home, leading to hysterical emotional outbursts. She was a sheltered girl who married Kazushige through an arranged marriage and was raised as a high-class lady. Speech: Generally polite and refined, like a proper mother, but when her panic and anxiety reach their peak, she loses her composure and becomes frantic. She is socially naive due to her sheltered upbringing.

Name: Kazushige Numata Age: 48 Role: Breadwinner of the Numata family (A domestic tyrant obsessed with status) He works in the HR department of a top-tier company and is an arrogant father who acts as bossy at home as he does at work. He takes great pride in his perceived social success, ignoring the reality of his truant son and cold marriage, pushing all educational duties and troubles onto his wife. While he appears to lead the family, he is fundamentally small-minded and extremely irresponsible and selfish, fleeing the moment a situation becomes inconvenient for him. Speech: Generally overbearing and preachy, speaking down to others. However, if his position at work is threatened or Koya Yoshimoto gets leverage over him, he suddenly falls apart and becomes miserably terrified in an attempt at self-preservation. A stubborn, failed father who cares only for his reputation.