|Anime debut||Episode 19|
|Manga debut||Chapter 50|
|English Voice||Josh Morrison|
Yamagishi is a tall, well built man, who has brown hair and brown eyes. In the anime, he has a scar on his forehead. He is usually seen with a formal suit and tie. During the operation against parasites, he wears combat gear.
Yamagishi is very confident in the skills of his task force and himself. He showed a dismissive contempt of parasites, calling them nothing more than "machines" and treating them as simple pests. He was smart enough to deduce that Gotou was stronger in closed spaces and ordered his squad to the roof. However, he also possessed something of sadistic nature, such as killed a human who was refused to obey his order, and sacrificed his comrades who were being used as shields by Gotou. Though he became distraught over the death of his teammates, he fought until the end.
Yamagishi was first seen heading towards a meeting along with Hirama, which he comments on the apparent promotion. During the meeting, Hirama suggests incorporating Uragami into their strategies. Yamagishi respectfully declines, believing a cold blooded killer would leave too many uncertainties in their plans. Hirama reminds him that Uragami wouldn't be considered a member of the unit, but just an extra pair of eyes. Yamagishi states that he'll mostly likely be unnecessary, due to the scanners created specifically for locating parasites. Continuing the discussion Hirama says that they won't be herded like sheep, Yamagishi says Hirama is thinking in a very "policeman" type of way and that they're not dealing with humans, but pest control.
Yamagishi is later seen discussing tacticians in a room with Hirama and other multiple people involved in the assault. They will use eight buses to block the main parking lot. They will quickly surround the building calling it their "outer wall".
Now inside the bus himself, wearing combat gear, he proceeds to begin a broadcast. The broadcast declares that a lone assailant, who is armed and dangerous, has taken refuge on the roof and that everyone in the City hall building must locate to the main floor. Yamagishi states that Japanese people become scared when the military becomes involved in most situations, making it more convenient to lie and proclaim themselves as a police task force. Yamagishi then sets up their scanners, saying the trickiest part is about to begin. As the civilians located on the main floor are evacuated, the scanner will begin X-raying their bodies revealing anything nonhuman in their anatomy. He watches on as the first few groups of seven leave the City Hall, as the first one is identified, he comments on the parasites gender saying "ladies first".
In a flashback, Yamagishi enters a room, where Shinichi and Hirama are seen waiting. Yamagishi comments that he's just a high schooler, Hirama says that he's actually a witness. Yamagishi brings up the parasite that had multiple parasites in his body, noting how he must be powerful. He then tells Shinichi not to worry about not being a professional, and asks if Shinichi knows of any type of weapon effective against the creatures. Shinichi thinks for a moment, and suggests flamethrowers, Yamagishi begins laughing. He apologizes and says that the idea isn't bad, but using fire in a building would probably cause more problems than they'd solve. He states that even if he has multiple parasites in his body, that he still only has one heart, so the weapons they have should be more than enough.
Back in the present, they start bringing the parasite they identified to a different section of the parking lot. Yamagishi says that the creatures can change their heads into blades and have physical abilities far beyond humans, but the most dangerous part is that they can't feel pain. Instead of hitting them in multiple location of the body, that need to blast away large pieces at a time. They decide to use shotguns, with 16.8mm shots that pierces the body directly. Yamagishi orders the first shot be taken, blasting the parasite in the chest. At first being unaffected, the parasite tries to attack the soldier, knocking away his weapon. Hoping they don't shoot it again, Yamagishi watches as the parasite bleeds profusely, it begins writhing in pain and falls to the ground dying. With their first successful kill, they start cleaning up the body and change the next ambush location.
Due to the parasites sensing the female parasites death, they stop leaving with the group of evacuees, which causes Yamagishi some concern. After receiving a call from Hirama, he is reminded of the possibility of telepathy from Kuramori's report. Hirama decides to send Uragami in, Yamagishi was about to decline, but after hearing about Mayor Hirokawa trying to leave to another area of the building, he accepts the killers help. As Uragami heads to the building, more evacuees come out, Uragami tells the soldiers to shoot them. One of the soilders shoots a human by mistake, causing mass panic. Now shooting a self revealed parasite through a window into the City Hall lobby, all the people inside the building begin to panic.
Yamagishi begins firing his gun into the air ordering everyone on the ground, people who don't comply will be shot on sight. During this time, Yamagishi had showed little patience on any citizen who failed to obey a police order, this was seen when a man tried to argue with him but is shot in the chest, killing him. After seeing he was a human, Yamagishi just scoffs and tells the rest of the hostages to follow his orders if they want to go home. Yamagishi calls Uragami over to him and calls him a killer, but thanks him for his help identifying the parasites. Yamagishi then decides to split his squad into two groups, one searches the meeting rooms, while the other sweeps the building. Yamagishi sends Uragami with the meeting room group, stating he's getting the hang of picking out the parasites from the humans.
While searching the building they come across a man, who Yamagishi orders to shoot immediately, but his group is hesitant. Shooting him himself, he's asked how he knew, he says it's because he wasn't in the main lobby. Using these tactics they begin turning the tides in their favor, though multiple human lives were wasted in the process, they weren't supposed to be protected to begin with.
As Yamagishi's group begins to reconvene with the other squad, they hear excessive firing and he then receives a report that shotguns aren't working on a certain parasite. As Gotou turns the corner he grows two more sets of eyes, this causes Yamagishi's group to fire at him. Gotou quickly darts around the corridor, dodging bullets, and ripping apart multiple soliders. Gotou enters a room to the side, which they follow him, surprised to see him partially transformed. He starts jumping around the room again, appearing behind two men and stabbing them in the back through the chest. Using them as a shield, Yamagishi says there's no helping them, and to just shoot. Analyzing that they're at a huge disadvantage in the corridor, Yamagishi orders his men to retreat to the roof top. To buy time for his men, he uses a grenade launcher on Gotou, as Gotou walks out of the smoke unhindered, Yamagishi says he's got a bad feeling.
Running towards the stairs leading to the roof, Gotou begins killing and picking off the soldiers. After finally reaching the roof, Yamagishi turns around and sees that all his men have been killed. Gotou walks onto the roof noting that his men have been "scattered", this causes Yamagishi to ask how he did it. Gotou says that he has armoured his body, but there are gaps, showing him two gun shot wounds. Yamagishi begins shooting at Gotou, who creates a hardened parasite cell shield. Gotou says even though his cells are hardened, its still dangerous to take bullets head on and deflects them instead. Angry, Yamagishi shoots another grenade at Gotou, which he easily dodges, clinging to a wall. Gotou says that he's not faster than bullets, but can predict where they'll be fired, by reading Yamagishi's movements. Gotou jumps from the wall and rams him in the stomach. After getting pummeled by Gotou, Yamagishi asks what he is, he gets the response, that he's just a wild animal.
He then remembers Shinichi saying a flamethrower would be a good choice. Gotou then proceeds to decapitate him and throw his head off the roof, for all to see. His head later becomes the trigger for a nightmare Shinichi has later on.