|Country of Origin||Japan|
|Family|| Daichan Aito (father; deceased)|
Reiko Aito (mother; deceased)
|Pathology|| Serial Killer (originally)|
Spree Killer (later)
|Signature|| Two distinct signatures:
|Victims|| 5 killed|
|Status||Deceased (shot by Garrett)|
|Portrayed By||Takashi Yamaguchi|
|First Appearance||Whispering Death|
"I gave them each an honorable death. Which is more than they deserved. My parents will finally be proud of me."
Yukio was ostracized by others for his tall stature and large weight. His parents owned a sushi shop at the Tsukiji fish market, and he was expected to inherit the business. However, pressure brought by the inheritance caused him to become a hikikomori, a severely withdrawn Japanese adult who seeks shelter in his own bedroom. His isolation contributed to his development of computer skills. Recently, the Tsukiji market was purchased by Taylor Investments, an American company, which led to the shop being shut down due to Taylor Investments' plans of redeveloping the market. This caused his parents to commit suicide using a legally-registered Japanese handgun. Upon hearing the gunshots, Yukio rushed out of his room for the first time in years and discovered his parents' bodies. Feeling guilty about not accepting his responsibility, Yukio projected his rage onto those who wronged his family business in some way and caused it to be shut down. He subsequently assembled a hit-list and started killing his targets consecutively, using methods of suicide in Japan.
By the events of the episode, Yukio had killed three people, and the IRT was called in to investigate at the behest of the U.S. embassy in Japan. At the same time, Yukio kills Akio Nakano. Afterwards, he is seen sitting in front of the computer in his bedroom with loud Japanese music playing. When he realizes the IRT had found the cameras he uses to record his killings, he begins to laugh. Afterwards, Yukio targets Kristopher Hall, the brother of his third victim. His first attempt to attack Kristopher is interrupted by the IRT, but Yukio later manages to kill him when he is alone in his hotel room. After Yukio is identified as the unsub, the IRT raid his residence, but he has already fled to a nightclub, where he sets his next target, Sean Kagame, on fire. The IRT show up, rescue Sean, and search for Yukio through the crowd of onlookers. When they find him, Seger speaks to him in Japanese, telling him that he can't run anymore and that he needs to think about his parents. Yukio removes the mask he had been wearing throughout the entire episode and tells her that his parents were ashamed of him. He then tells Garrett that his parents will now be proud of him since he gave his victims honorable deaths. However, Garrett tells him that there is no honor for what he did. Seger then tries to convince Yukio to turn himself in, but he replies that he isn't done yet, pulls out his parents' gun, and tries to kill Seger. Garrett shoots him in the head first, killing him instantly and horrifying all of the onlookers.
Yukio targeted people who were in some way responsible for causing his parents to lose their sushi bar business and causing them to commit suicide. He would find them in the Tsukiji fish market, stalk them, blitz-attack them when they were in vulnerable positions, and then kill them using a variety of methods based on traditional Japanese suicide methods. Yukio would then set up cameras at the crime scenes so they could stream live footage of the aftermath to his own computer, in order to relish his handiwork. During the nightclub standoff, he was armed with a Nambu Type 14 pistol, a World War II-era Japanese pistol, which was legally registered to his family.
The unsub is a Japanese resident between the ages of 25 and 35 who is familiar with the Tokyo region. Based on his ability to overpower his victims and positioning of their bodies, he is six feet tall and weighs 140-160 pounds. This implies that both his height and weight cause social problems, as they would make him stand out in the crowd and therefore be ostracized. The fact that he records his murders means he is technically sophisticated and does this to admire his crimes. His propensity towards voyeurism and the nature of his attacks indicate that he is incapable of normal social interaction and is unemployed. The staging of the bodies is his way of trying to purify his victims by giving them what he believes to be an "honorable death". The slot in the unsub's room, abundant dirty dishes and take-out food indicate that he is a hikikomori, a young Japanese man that retreated into his room, cut all social ties and spends his time watching TV or surfing the internet due to being ashamed of not living up to social pressures. Since he can't go back home, he will be at the site of the last murder, watching and not filming. After years of isolation, he will probably have a Vitamin D deficiency and exhibit rashes and rickets. He will also stand alone and his body language will appear stiff and distant because he isn't used to crowds.
Yukio appears to be based from Hiroshi Maeue, a.k.a. "The Suicide Website Murderer", a Japanese serial killer who took advantage of traditional Japanese views on suicide and used the Internet to find his victims. The main differences were that Maeue's victims were all Japanese and had contacted Maeue because they wanted to die, just not in the painful way that Maeue killed them. Like Yukio, Maeue was unemployed at the time of the murders, killed his victims by strangulation, and recorded his crimes to extract further gratification. Coincidentally, Yukio shares his first name with Yukio Yamaji, a Japanese murderer who was executed next to Maeue.
- September 22: Dee Brown (was planning on moving out of the apartment subleased by his father; tied her knees together and slashed her throat; based on the Jigai suicide method)
- September 26: Bobby Freeman (wrote a bad review about the fish market; thrown in front of a bullet train; based on the Tobikomi suicide method)
- September 28-29: Damian Hall (involved with Taylor Investments; hanged; based on the Kubitsuri suicide method)
- September 29:
- Akio Nakano (quit his job at his parents' business; stabbed in the stomach and disemboweled; left his body posed in a freezer; based on the Seppuku suicide method)
- Kristopher Hall (Damian Hall's brother who was also involved with Taylor Investments; stalked and intended to kill; was interrupted before he could act)
- The hotel attack:
- Kristopher Hall (thrown out of a high-story window)
- Unnamed security guard (incidental; assaulted while escaping)
- September 29-30: The nightclub attack:
- Sean Kagame (the co-owner of Taylor Investments; attempted, but barely survived; assaulted and set on fire, but it was put out)
- Clara Seger (incidental; attempted to shoot with a Nambu pistol)
- Note: Yukio also had another victim on his hit-list named Jarod Taylor, who co-owned Taylor Investments, but he never managed to attack him due to being interrupted at the nightclub.