Lemon's Copper Wire

Lemon's Copper Wire is an improvised latch that can lock a Shinkansen toilet door from the outside. Its importance lies in how an ordinary, functional scrap of metal becomes evidence: Tangerine recognizes Lemon's familiar trick in the wire, and the copied method points toward another person at the scene of the deaths. Later, Nanao uses the same mechanism, extending the wire's role from clue to instrument of concealment.

Appearance and operation

The wire protrudes from the toilet door, visible enough for a schoolkid to point it out as something strange. The door appears locked and its indicator says occupied, although the child hears no sign of anyone inside. That mismatch makes the wire more than a hidden part of the door: it is a small, exposed explanation for a larger uncertainty about what the locked compartment contains.

The mechanism is direct. Tangerine takes the end of the wire and pulls it upward; the lock releases with a clack. Later, the schoolkid tells Nanao that pulling the wire will open the door, and Nanao confirms this by doing so. After arranging things in the bathroom, Nanao fumbles with the wire until he manages to lock the door again. The same piece of metal can therefore control access in both directions, without a key or any elaborate device.

Lemon's method and Tangerine's deduction

Tangerine recognizes the wire immediately as the same kind Lemon used to secure a toilet door from outside while hiding Little Minegishi's body. The recognition is exact and practical: this is not merely a similar-looking scrap, but the trace of a technique Tangerine knows Lemon used repeatedly. When he pulls the wire to open the door, the familiar mechanism reveals what the occupied sign had concealed: bodies are inside, thrown together in a grotesque heap.

The wire also unsettles Tangerine's reconstruction of events. He considers the possibility that Lemon shot the other man, put the body in the toilet, and locked the door using his usual trick. But if Lemon was then shot and placed in the same compartment, the door must have been locked again after his death. Tangerine sees that the wire does not fit a sequence in which Lemon alone handled the bodies and the door.

His inference turns on how a technique could be transmitted without instruction. Whoever locked the door the second time must, Tangerine reasons, have seen Lemon use the wire first and copied what he did. The wire thus preserves a sequence that the bodies themselves cannot establish: Lemon's method was used, and then someone else repeated it. Tangerine's attention to the wire redirects his account of the scene from a simple exchange of gunfire toward the presence of an additional participant.

Nanao's use of the wire

The mechanism recurs when Nanao comes to the bathroom with the schoolkid. The child explains that people were shooting each other and indicates the wire as the way to open the door. Nanao follows the instruction and finds two bodies inside, discarded together. The wire gives him access to the hidden scene, much as it had enabled Tangerine to enter it earlier.

After retrieving the suitcase from the crew room, Nanao returns and finds Tangerine pointing a gun at the child. Once Nanao has dealt with the bathroom and arranged things inside, he closes the door and works the wire until it catches. The action repeats Lemon's method, but now Nanao is the person using it. The resemblance does not establish that Nanao witnessed Lemon's earlier use; rather, the scene shows that the simple trick can be learned and reused, just as Tangerine had concluded someone must have copied it.

Evidence, concealment, and recurrence

The wire's significance comes from the tension between its modest appearance and its consequences. It is only a length of copper sticking out from a train toilet door, yet pulling it exposes a hidden collection of bodies, while lifting it again can conceal them behind a locked door. Its physical simplicity makes the method reproducible: a person does not need Lemon to teach the trick, only the chance to watch him use it.

As a result, the wire serves two different kinds of knowledge. For Tangerine, it is a forensic trace that prompts a more complex reconstruction of who handled the bodies and when. For Nanao, it is an immediately useful mechanism that opens the bathroom and later lets him secure it. Across both encounters, the object shifts from unnoticed hardware to an object under scrutiny, then back into use. That movement makes it a compact link between the concealed scene, Tangerine's reasoning, and Nanao's later actions.