
In Death Note, Watari is L’s assistant. He is also the person responsible for providing tools to support the Japanese Investigation Unit.
APPEARANCE Watari Death Note

Watari has blonde hair and blue eyes. When he was spotted by Interpol officials in the role of L’s assistant, he wore an overcoat and a hat that covered his face. After revealing his face to the Japanese investigating unit, he wore a black tuxedo with glasses.
PERSONALITY Watari Death Note

In the normal course of everyday life, Watari is famous for his inventions and is the creator of Wammy’s House, an orphanage that caters to gifted children located in Winchester, England. L was also a resident of the orphanage.
Watari served as his father figure prior to the beginning of his detective career. He is also a skilled spy and a sniper. As per Death Note 13: Learning to Read, Watari likes grey tea and is averse to dirty rooms. When communicating with others on computers, Watari appears on a white background, with the letter W written in black “Cloister Black” font, similar to the way L used to write the letter L.
PLOT
THE START OF THE KIRA INVESTIGATION

In the fall of 2003 (animated in 2006), when a meeting of Interpol found out that criminals had died from heart attacks, and when the participants considered deferring the matter to L, Watari informed the group that L had begun an investigation before. He then pulled out his laptop and used it to conduct an investigation. L was able to use it to address attendees of the meeting.
In the beginning stages of the investigative work of the NPA of this elusive serial killer (publicly called Kira), at the request of L, Watari was frequently at the offices of the investigating unit using his laptop. Just like in the Interpol meeting, it was via this laptop that L addressed the members of the investigating unit. Watari generally left the NPA office once L engaged in a private discussion with him.
However, after twelve FBI agents who were to watch for the Japanese police and loved ones lost their lives, those who believed their lives were important were removed from their position in the Investigation Unit. Six officers were left and they were not all able to trust L. The reason for this was mostly because officers could only talk to L via his laptop without knowing his name or face. Watari provided L with written instructions on what to do in order to reveal L’s face.
SHOWING THE FACE

On New Year’s Day 2004 (Anime 2007), L had just presented to the Imperial Hotel all the information that was gathered through the FBI and had concluded an in-depth interrogation of every officer within the investigation unit. The moment came that Watari himself was inside the room, dressed in an undercover uniform, as in the absence of it, L’s location would be revealed to the public and to prove his trust in the personnel of the investigation unit again.
Watari was also carrying along with him some accessories for members of the investigating team. First, there were fake badges that police officers needed to wear in order to shield their identities from the prying eyes of all who came near them. The second was a belt with transmitters attached to the buckles which could be pulled to activate Watari’s phone. If his phone would respond to the call, he would return and inform the people about the location of L’s phone.
SURVEILLANCE CAMERAS AND LISTENING DEVICES

Watari was in the hotel’s room when Hirokazu Ukita made a phone call to them by Naomi Misora’s mother concerning their daughter’s disappearance. Naomi Misora was engaged to one of the deceased FBI agents, Raye Penber. Since Penber was acting oddly prior to her death, L decided to limit the investigation to those who were investigating her. They were the families of NPA Deputy Director Koreyoshi Kitamura and Police Chief Soichiro Yagami. Yagami was also a part of the Kira Investigation Unit.
Watari set up surveillance cameras and listening devices in these homes within the next day. The first day, Watari, following the advice of L, also granted permission to every channel to air a false message over the TV image concerning the arrival of 1500 Interpol detectives from Japan to observe how individuals under monitoring would feel about the announcement. The operative also handed over to the unit investigating the incident the names of the criminals who had been killed that night. In the course of five days of monitoring, Watari was able to remove the cameras as well as listening devices.
LIGHT YAGAMI’S SUSPICION AND ANOTHER KIRA

When L was able to infiltrate To-Oh University to observe Light Yagami, Watari posed as his chauffeur. After Light Yagami agreed to join the unit upon request of L, Watari and Mogi were required to stay in the hotel and pose as the second L to anyone who came by. They only spoke to fellow members of the team whenever new information was received through the other Kira. The communication was later handed over to Watari by himself, as Mogi had been assigned to watch Light.
When the Kira investigation team discovered clues to Kira inside Misa Amane’s bedroom and were able to arrest her on suspicion of having been an additional Kira, Watari was assigned to look after Misa. L instructed Watari to do whatever was necessary to get Misa to speak and he was also instructed to be careful. Watari did not provide Misa the water she needed for 3 days. He also was unable to control her when she threatened to bite her tongue.
Then, Watari also prepared cells for Light and Soichiro as Light had become the primary suspect in the case of the real Kira and Soichiro was ashamed of the suspicions he had against his son.
In the event that it was decided to alter the method of surveillance for Light and Misa, the investigation team relocated to a new headquarters designed in the name of L and Watari.
YOTSUBA

Watari was the person in charge of security in the headquarters’ new building. Security measures included an eye retina sensor as well as metal detectors. L also told Light the fact that Watari was among the other people in the role of L.
After discovering that Kira was a shrewd businessman at the expense of Yotsuba Group, Watari was able to gain an inside look through his connections to the world of business. He also provided assistance to the members of the investigation team in the event of being exiled from the police, which was the situation when the NPA had to end the investigation of Kira. After all but Shuichi Aizawa were left within the team of investigators, Watari was assigned to call two of L’s underworld friends, Aiber as well as Wedy, to aid the investigating team.
Because Watari also served as a liaison to the third and second best investigators, Eraldo Coil as well as Deneuve (who had been L’s pseudonyms), he was able to give L the details about Masahiko Kida, who was the Yotsuba’s director of the Legal and Planning department, employed Coil to determine the identity of L. Following the time that L had instructed Aiber to pretend to be Coil in front of Yotsuba, Watari was to aid Wedy install surveillance cameras as well as listening devices in Yotsuba headquarters.
After narrowing the suspects down to seven in the secret meetings, Watari and Wedy added camera systems and listeners in their places to watch the suspects. However, the task was made a bit more difficult due to being aware that Shingo Mido, Reiji Namikawa as well as Kyosuke Higuchi were very secure in their residences.
With Higuchi identified to be Yotsuba Kira and L setting up plans to capture Higuchi, Watari initially relayed mainly only a phone call with Mogi with Higuchi to the headquarters. However, when Higuchi suddenly appeared to require only a face for his victims these days, L gave the order to take down Higuchi. Watari was with him, as well as Light via helicopter to join the hunt. Watari, carrying the sniper rifle, was used to kill Higuchi. Higuchi attempted to flee. In the beginning, when he tried to escape the police vehicles and the Kira investigation team, Watari shot a tire from his vehicle. Then, when Higuchi threatened to kill himself, Watari shot the gun from his hands.
DEATH

In the wake of Higuchi’s mysterious demise and L’s speculation regarding his Death Note notebook that was later discovered to be a weapon for murder, Watari was ordered to locate a country that was willing to utilize the notebook for an execution. He also was required to prepare to pack the notebook to be transported.
However, before that could be accomplished, Rem, a shinigami worried about the security of the victim he was killing in the name of the present Kira (aka Misa), wrote the name of Watari in his notebook to take him down. Rem was then able to kill L himself.
It was the Kira Investigation Unit that later learned Watari’s true identity after the murder of his wife, a civilian, Quillsh Wammy, was published in the local newspapers. Apart from Wammy’s family and the Kira Investigation Unit, only the Wammy’s House orphanage were aware of his identity in the form of Watari.
LEGACY Watari Death Note

As the new L, Light Yagami (who was also the real Kira) was also Watari up to her demise. Following the demise of Watari, Roger Ruvie, who was also the house’s leader, was named Watari following the death of Light Yagami and Near became the new L.