Lin Xianming is a nineteen-year-old trained assassin originally from the slums of China. He was raised in extreme poverty alongside his mother and younger sister after his father abandoned the family, leaving behind gambling debts. To relieve his sick mother of the burden of supporting him and his sister, he voluntarily sold himself to human traffickers at the age of nine. He was placed in a facility where children were trained to become killers, filling the position of a recently deceased trainee. There he met his roommate and first friend, Feilang, and the two supported each other through four years of brutal instruction. On the day of their final examination, they were locked in a room with weapons and ordered to fight to the death. Feilang attacked him first, and in self-defense Lin struck him with a nearby object, inflicting a deep wound. Believing Feilang had died, Lin was released and shortly afterward began working as a professional hitman. About a year later, he was sent to Fukuoka, Japan, to work under Zhang, an executive of the Kakyuu Association.

Lin is a blunt, self-reliant individual who has difficulty trusting others due to the betrayal he experienced and the harshness of his upbringing. He tends to speak curtly and can come across as insensitive, but this stems from a conviction that harsh truths are better than comforting lies. He is also conscious of money and never wastes food, habits rooted in his childhood poverty. Despite his guarded nature, he has a strong interest in fashion and romance stories, and he spends money on shopping as a way to relieve stress. He is impartial to conventional gender norms, openly wearing women's clothing, makeup, and skirts because he sees no reason why men should not wear what women can wear. This practice also serves as a way to feel closer to his younger sister, from whom he was separated for nine years. He has long light-brown hair, androgynous features, and is often seen in a brown vest over a white chiffon blouse with a red ribbon, a red skirt, and black socks.

His initial motivation in the story is to pay off the debt he owes to Zhang, which keeps him bound to the Kakyuu Association. When a target commits suicide before he can complete the kill, he is refused payment. The organization then orders him to assassinate private investigator Zenji Banba, believing Banba is interfering with their operations. Instead of carrying out the hit, Lin protects Banba from another attacker. Banba discovers the debt and pays it off, freeing Lin from his obligation to the organization. After this, Lin begins freelancing as an assassin and lives with Banba, effectively freeloading off him. He becomes a member of the Hakata Tonkotsu Ramens baseball team, which serves as a cover for a group of underworld professionals. Over the course of the story, Lin learns to open up and trust others, a gradual development that begins with his alliance with Banba and extends to the broader circle of associates they work with. His key relationships include his bond with Banba, who becomes his closest ally and the person who helps him break free from his past; his complicated history with Feilang, whose betrayal left lasting emotional scars; and his ongoing search for his missing sister, which motivates many of his personal decisions. His notable abilities are his expertise with bladed weapons and his honed skills as a professional assassin, trained from childhood in a ruthless environment.