|Occupation||High School Student|
|Relatives||Kiichi Kato (father, deceased)|
|Manga||0001. An Incident|
|Live Action Actor||Kenichi Matsuyama|
Masaru Kato (加藤 勝, Katō Masaru) is the secondary protagonist in Phase 1 and primary protagonist in Phase 2.
He is tall, with long black hair back (No one knows how his physique is since he is never seen without a shirt). He wears clothes in a stripped-down style
Kato is known by the entire Gantz team for his altruism and gentleness, using force only when necessary (also known as a gentle giant according to Kishimoto). Throughout the series he is constantly looking for a second way to end the game instead of simply killing the aliens and always trying to find a way for all players to come back alive. Although he tries to be a pacifist, he has shown himself to be violent when necessary, an example being when he assaults Onidzuka without warning after the latter expressed a desire to rape him, with Masaru being visibly nervous in class once he finds out.
After seeing a homeless man named Takao Tadō fall on the subway track, Masaru Kato goes down to help him. However, the man is too heavy to be carried to the platform alone, so he calls out to his childhood friend Kei Kurono who he recognizes in the train station to help him which he reluctantly does. Horrifically, after getting the man on the platform the subway comes and rips them apart, killing them. Instead of moving on they find themselves in a strange room along with 6 other people and a dog whom also apparently all recently died. Suddenly, a naked woman appears on top of Kurono after committing suicide in a bathtub. There is a mysterious Black Sphere in the room that starts playing an old exercise song and tells them to hunt a little alien. The ball opens up, displaying weapons and suits which they take. They are then transported out of the room. Masaru originally tries to stay with Kurono and Kishimoto (the girl who appeared on top of him), but he goes off to try and protect the child alien, finding himself helpless to prevent its death. The father then shows up and proceeds to make short work of the other four people there before facing down Masaru who tries to reason with it and apologize to it, to no avail. The alien starts chasing him and knocks him down a hill Before he can go after him, Kurono shows up and gets it to chase him. Masaru, waking up at the bottom of the hill, makes his way back towards where he was. He sees Kurono jump away from the alien which is chasing him down. Luckily, right before it can kill Kurono, Masaru gets his arms around it in a headlock. The alien responds by shredding his arm and breaking his wrist to get loose and smashes him to the ground. While he is bleeding out on the ground the angry alien approaches and picks up Masaru's body ready to strike the finishing blow. Kurono then gathers all his strength to beat the alien. After he beats it senseless, a middle schooler named Nishi appears after being invisible and offers Kurono the points at which point Masaru passes out. As the others are transported back to the room, Masaru is seen twitching showing he is still alive. However, he only remembers what happened up until he was about to grab the alien. Kurono and Masaru then demand explanations but Nishi is reluctant to answer them and eventually disappears, going invisible again. Subsequently, they go home in a taxi, with Masaru going home after Kurono and Kishimoto.
During his third mission, the Buddha Temple mission, the final boss kills him. He, along with Kishimoto, Hojo, Sadayo, Sei and other Gantz replacements, die in this mission, leaving only Kurono alive.
Six months later, he is revived by the 'Old Man'.
At the end of chapter 237, in the preview for Phase 2, Kato states that he will revive Kurono from his death, no matter how long it takes. On his first mission since his revival, he and the rest of the team end up in Osaka instead of Tokyo and meet up with the Osaka Gantz team. Kato continues to act as leader, although the team had earlier decided on making Reika leader.
In chapter 247, Kato is abandoned by his Tokyo Teammates after Sakata Kenzo states that their main goal for this mission should be to stay alive and that Kato should forget about Kurono as well as the innocent civilians being killed. After the falling out Kato begins to doubt himself, but becomes convinced once again after he nearly lets a family be killed by not acting. He then meets Yamasaki Anzu, a female member of the Osaka team and learns more about the Osaka team and the rare 100-point alien. After rescuing Yamasaki and three other unwitting Gantz participants, Kato vows to kill the "100-pointer" and revive his best friend, Kurono.
In recent chapters Yamasaki makes Kato promise that he and his little brother will move in with her and her son. In turn, she promises to make sure he does not die. Kato is successful in killing the 100 point alien, and uses the points to revive Kei Kurono.
After defeating the 100 point alien and reviving Kurono, he shows great concern after Nishi tells them the "End of the World" in 1 week's time and is seen at the meetings regarding that issue. In chapter 285, Kato encounters the original Kishimoto at a train station and tries to ask her out, to her amusement. It is unknown if she accepted or not.
Surviving the Italian mission, Gantz sets Kato and the rest of the hunters free. In chapter 303, Kato is seen in his classroom clearly worried about the Katastrophe. Kato later runs into Nishi in front of Shinjuku station whilst waiting for Ayumu. Kato asks Nishi why he is smiling at a time like this, Nishi replies that everything is about to be turned upside down. Kato tells him that he is not normal, which Nishi retorts that Kato couldn't care less if everyone around them died at that exact moment. Their conversation is interrupted by the arrival of mecha falling from the sky. Kato later saves children from a robot that is attacking them, using the Y-gun to wrap it up and sent it away. Kato and the others are transferred to another location.
After a brief scuttle between participants (resulting in a few deaths), they are then transported to yet another location. Kato is confused about where they are and why they are there. When one of the people of the front of the group earlier tells them the situation, ordering them to shoot the potential invaders after they get noticed, Kato yells at the other hunters not to shoot, but is forced to fight after the aliens attack him and the others. One of the aliens (the one that is targeting Kurono) appears before Kurono and Kato yells for Kurono to run. Kato appears with the others after the transfer. The leaders decide to send the hunters to different areas rather then send them to where they were first transferred from. Kato is sent to an area alone where the city can be seen in the distance.
Later on he manages to meet up with Kurono clone, Reika, Kaze and Takeshi. They all decide to head to the Gantz room in hopes of getting in contact with Gantz. They trek up the building and enter the room to find the black ball closed and not responding to them. He is present when Nishi explains about the Gantzers that transported them and has the bomb removed from his head. When Kei and Reika communicate with the other players and get a response, he wonders if someone is being transferred to the room. He watches as a male player gets transferred in. When Hyouma Takeda introduces himself, he jealously asked Kato if he was Reika's boyfriend. Kato, taken aback by this statement, denies accusation. Tthe last two players are transferred into the room, one of them being the nerd that promised to bring back Anzu Yamasaki. When he sees Kato, he begins to cry and tells him that he kept to this promise. Kato watches as she is transferred into the room and they have a tearful reunion.
Kato and most of the Katastrophe Team (omitting Nishi and Takeshi) are transferred up into the giant spaceship and they start rescuing people. The team manages to rescue quite a few people, but when they get back to the room, they discover that they haven't rescued that many people at all. They formulate a plan and head back up to find more of these "meat processing plants". Kato and the others head to another one and after rescuing all of the people there, they plan to move on to another one. Ryuuji requests to wait until he does something and goes and urinates in the pool where they rescued the people from. He is joined by the other male teammates, including Kato, much to the shock of the female teammates. After a while when some of the people have been transferred, a giant two headed monster and three giants crash through the wall. The team proceeds to fight off the monster and they succeed in killing the monster and the three giants.
The transfer stops and they wonder what is going on. Once the transfer had started up again, the team and the survivors get transferred to an unfamiliar area. The team formulates a plan and Kato tries to convince the survivors not to stray away from them. Anzu and the nerd offer to try and convince them.
Kato is seen fighting alongside Kei.
Frequently, Gantz addresses him as "Katō-cha", after the Japanese comedian, Katōcha. One translation of this is Kato-cha.