The Garden of Sinners: A Study in Murder (Part 1)

Shiki's nocturnal wanderings stem from her dissociative identity disorder. When she encounters the corpse of a traffic accident victim, she enters a trance-like state and applies the blood to her lips, a behavior connected to her SHIKI personality, which represents her repressed, darker impulses. This act marks the beginning of her involvement with the murders, as the blood triggers something within her.

The murders are committed by Shiki's alternate personality, SHIKI. While Shiki's main personality remains unaware or detached, SHIKI is the male alter ego that represents her violent and rebellious impulses. When SHIKI takes control of her body, he carries out the brutal killings. The police find Mikiya's school emblem at a crime scene, which complicates things, but the killer is fundamentally Shiki herself, specifically her SHIKI personality.

Shiki has a rare condition known as dissociative identity disorder, inherited as the successor to the Ryōgi family. Her main personality is the shy, withdrawn Shiki, but she also possesses SHIKI, a male alter ego that embodies her rebellious and violent impulses. These two personalities are often out of sync, with SHIKI sometimes taking control of her body without her awareness. This condition is the key to understanding the mystery.

When Shiki shows Mikiya her bandaged arm and admits it happened during the latest killing, she is being controlled by SHIKI at that moment. This admission is a deliberate provocation, SHIKI wants Mikiya to understand the truth about her violent nature. It's a test to see if Mikiya will accept her despite knowing what she is capable of doing.

Mikiya's detective cousin Daisuke reveals that police found Mikiya's school emblem at the latest murder scene. This creates a dangerous situation for Mikiya, as he becomes a potential suspect. However, the emblem's presence is likely coincidental or planted, Mikiya is innocent, but the discovery puts him in a precarious position and creates tension with his cousin who is investigating the case.

When Mikiya arrives at Shiki's mansion and finds her drenched in blood beside a beheaded corpse, SHIKI is in control. Rather than fleeing or hiding, she approaches him deliberately, this is SHIKI testing Mikiya's reaction and forcing him to confront the truth about her. It's a moment of vulnerability where she reveals her darkest side, giving him a cryptic warning about her nature.

Despite discovering Shiki's involvement in the murders and the obvious danger, Mikiya returns to her house each night because he cannot abandon her. His feelings for her are genuine, and he chooses to believe in her even after seeing her drenched in blood. This reflects his fundamental character, someone who offers unconditional support rather than judgment, even when reality becomes terrifying.

During the climactic confrontation, Shiki chases Mikiya to an outside road and holds him at knifepoint. When she demands he say something to stop her, Mikiya simply states he doesn't want to die. This honest, non-judgmental response contrasts with what SHIKI expects, rejection or fear. The moment reveals that despite knowing Shiki is dangerous, Mikiya cannot bring himself to condemn her.

By June 1998, Shiki has become comatose and is hospitalized. While the exact cause is not explicitly detailed in this summary, her coma results from the traumatic events surrounding the murders and possibly her own self-destructive tendencies. The violent life she led, split between two personalities committed to murder, appears to have taken a severe toll on her physical and mental state.

Mikiya visits the comatose Shiki in 1998 with flowers and tells her he has always believed in her. His belief is not blind, it comes from seeing the genuine, kind side of Shiki that exists alongside her SHIKI personality. He understands that the murders were committed by her alternate personality, not her true self. His unwavering devotion represents the film's thematic center: choosing to believe in someone despite their darkness.

Shiki's relationship with Mikiya is complicated by her dual personalities. When SHIKI is in control, he appears boyish and behaves differently, sometimes even asking Mikiya out on dates in a masculine manner. This confuses Mikiya, who doesn't understand why Shiki acts so differently at times. The shifting dynamics reflect the central tension: Mikiya is drawn to Shiki, but he can never be certain which personality he is interacting with.

SHIKI cryptically warns Mikiya that Shiki will kill anything that 'opens up her isolation with the world.' This means that any relationship or connection that threatens to pull Shiki out of her solitary, isolated existence becomes a target for her violent alter ego. Mikiya, as someone trying to connect with Shiki and bring her into the world, represents exactly that threat, which is why SHIKI warns him while also preparing to eliminate him.