Weapon

Weapon (武器, Buki) is the fourth chapter of volume four and the twenty-ninth chapter of the Death Note manga series.

Plot
In her apartment, Misa Amane has been using the internet and been getting plenty of information on Light Yagami whom she identified as Kira after luring him to Aoyama. Although she can find no photos of him, she learns about his successful sporting and academic achievements and will use this information in order to find his address. She is equally delighted at how handsome he is!

On May 25th, the Kira Task Force, including Light and L, meets to discuss the visits to Aoyama on the 22nd and Shibuya on the 24th. Neither visits yielded much results. Their only option left is the Tokyo Dome which the diary mentions as where the writer saw a Shinigami.

Light wonders how he is going to be able to see the Second Kira's Shinigami without touching the appropriate Death Note. Ryuk has already made it clear that he will not inform Light about the presence of other Shinigamis in the human world. Light wonders if it is really up to him to come up with a way to make contact. L himself is thinking along similar lines: That it is up to Kira to lure out the Second Kira.

Suddenly Watari contacts the group through L's laptop and informs them that the Second Kira has sent yet another video. He puts it through to them. In the new video, the sender claims to have found Kira and thanks the police and media for their assistance!

Light is astonished because he took precautions in order to be sure that even if the Second Kira's Shinigami had seen Ryuk it would not have been possible to link him to Light and Light also kept a sharp lookout for anyone following him.

The fact that the video was sent in an envelope postmarked on the 23rd leads L to believe that this happened on the 22nd at Aoyama, the day Light went there himself. Add that to the fact that FBI agent Raye Penber was investigating Light at the time of his death and this only strengthens L's suspicion that Light is Kira!

The other detectives worry that the Kiras have joined forces, but L points out that "found" is not the same as "met" so they can assume that the Kiras have not yet actually made contact, especially since the original Kira is unlikely to allow such an event to be made public in this way.

The Second Kira has already killed a number of people so immunity from prosecution is out of the question. Still, L suggests making an official police appeal to the Second Kira for information on the real Kira, with the offer of a lesser sentence and the fact that the Second Kira will be seen as a hero for bringing an end to Kira's reign of terror.

Light faces agonizing dilemmas. The Second Kira is clearly unreliable, otherwise why make such a public announcement? Light has also guessed that L has narrowed the encounter down to Aoyama. Is the Second Kira really trying to help Kira? Or could he take the bait and betray Light?

That night a police appeal goes out on the evening news urging the Second Kira to provide them with information about the real Kira. Misa watches the announcement and gasps at the warnings, especially that Kira may use and kill her. She dresses up and, followed by Rem, leaves her apartment.

Misa arrives at the Yagami house where she introduces herself to Light's sister Sayu and claims that she is returning a notebook which Light left behind at university. Sayu calls for Light. When he takes the notebook, Light sees the monstrous Shinigami Rem and realizes who Misa is.

Sayu and their mother assume that Misa is a girlfriend Light mentioned when explaining his returning late home one evening—actually due to being with the Kira Task Force. They have not touched the notebook and thus cannot see Rem.

Light invites Misa into the house and takes her up to his room. Once they are alone he asks how she managed to track him down. Misa explains that she has the Shinigami Eyes but that in the case of fellow Death Note owners she can only see their names, not their life spans. Light gives Ryuk a hard stare and the latter admits not knowing that detail.

Misa explains why she came to see Light: She offers to be his "eyes" if she can be his girlfriend! Taken rather aback, Light chooses his words carefully for fear that she might kill him. He explains that there were security cameras all over Aoyama on the day Misa first saw him. If she was spotted in Aoyama and if they are seen together in future then this could raise the police's suspicions. Misa tells Light that she has been careful in her undertakings. She shows him pictures of the schoolgirl disguise she used in Aoyama and explains that she got a friend to handle the Kira tapes and send them to Sakura TV in the belief that they were occult videos. Thus, her fingerprints are not on anything incriminating. In order to further gain his trust, she offers him her Death Note, Rem confirming that Light can keep but not claim ownership until Misa renounces it or dies. What's more, Misa tells Light that he can use or even kill her if she becomes a burden!

Light is amazed by the lengths at which she is going to. Misa explains that her parents were murdered in her presence over a year ago. The killer never came to trial due to judicial delays but was then killed by Kira! She is grateful to him for that.

Light points out that she killed innocent people—(something he himself has done). Misa replies that she was desperate to meet him. Light has to admit that the way she covered her tracks indicates that she is not as stupid as he originally thought.

Light tells her that although he is not fully committed to being her boyfriend, he will at least try and play the part. She will be a valuable weapon. Misa is grateful for this and will do what she can to earn his love. They hug.

Conception
The title "Weapon" refers to Light's idea of using Misa as a "weapon" to kill L. Misa even accepts Light's attitude towards her.