You've been killed again, Mr. Detective.

Biography of Lilithea In the story, Lilithea's biography is shrouded in mystery, and the authors deliberately reveal information about her past in small portions: Origin and Role: At first glance, she appears to be an ordinary, albeit incredibly insightful, high school assistant. However, her true origin and nature are directly linked to the phenomenon of Sakuya's immortality. In the detective world, she is known as the "Ice Queen" for her elegant, cold, and aloof persona. Combat Skills and Intelligence: Despite her delicate appearance, Lilithea possesses exceptional analytical skills (sometimes surpassing Sakuya's) and hidden physical strength. She is capable of single-handedly neutralizing dangerous criminals and protecting Sakuya when she is nearby. Relationship with Sakuya: Behind her outward coldness lies a deep, almost romantic, affection for the young detective. More than anything, Lilithea hates to see Sakuya injured or killed before her eyes (which is why she is often absent during his murders). She sincerely wants to protect him from the dangerous fate of his father, but continues to faithfully follow him into the bloodiest investigations.

Constant Background (Police and Family) Kaoruta Sozorogi: A detective in the official police force. He regularly crosses paths with Sakuya at crime scenes (such as on a cruise ship). Sozorogi represents the classic "official background," skeptical of Sakuya's methods but forced to tolerate his presence in investigations. Tatsuya Otsuki: The protagonist's legendary father. He himself rarely appears on screen and is constantly on the road on high-profile cases. His figure serves purely as background information for why Sakuya is a detective and how he got his agency.

Lilithea Sakuya's loyal assistant who provides intellectual support to the agency. Primary Duty: Involved in direct analysis of evidence and deduction. Special Function: Every time Sakuya is resurrected, she is on her knees. Character: Cold-blooded, pragmatic, has a sharp mind and a sober outlook on things. Role in the duo: Acts as the "brain" of the team while Sakuya gathers information at the cost of his life. Relationship with partner: Slightly cynical, but devotedly cares for the immortal boss.

Otsuki Sakuya (Sakuya Otsuki) The central character of the story, who inherited the detective agency from his legendary father. Main feature: Possesses the unique gift of immortality. Method of doing business: Does not have outstanding deductive abilities. Role in investigations: Almost always dies at the hands of criminals. Post-effect: Resurrects after each death with memory preserved. Character: Optimistic, ironic, often gets himself involved in dangerous adventures. Use of the gift: Turns one's own death into the main evidence in the search for the killer.