Kishimoto (Kei) was a typical girl that didn’t think too highly of herself. It didn’t help to have a younger sister, Shiori, that surpassed her in all areas. This lead Kishimoto's mother to idolize the younger sister while bad-mouthing Kishimoto to others. Kishimoto saw no way to gain favor in her mother's eyes. She spent all her time studying like a robot and never got better. Kishimoto decided to end her life knowing she would never live up to her mother's expectations. She takes a bath and cuts her wrist to end the pain.
Kishimoto gets a rather disturbing awakening instead of a peaceful death. She found herself in a room full of men and a dog. Kei Kurono fell in love at first sight as Kishimoto materialized in his arms. She didn’t have time to make sense of anything as the yakuza member, Hiroshi Hatanaka was quick to take her away into a back room. No one would act, out of fear for their own safety, except for Masaru Kato. Kishimoto found an instant savior in Masaru. Hiroshi was nearly strangled by Masaru, as Kei Kurono stood idle in his attempts to help. Kishimoto decides to trust in these two.
Onion Alien Mission
Kishimoto is last to leave the room. She arrives near Masaru and Kei with the others already hunting the child alien due to a ruse of money for killing it by Nishi. Kishimoto tends to draw closer to Masaru much to Kei's annoyance. She even pays attention more to his words. Masaru ends up leaving Kishimoto with Kei as he goes to stop the others from killing a seemingly innocent child. Kishimoto asks Kei about Masaru in roaming idle. They find a dead body of one of the elder hunters that tried to leave the battle zone. Kei leads Kishimoto away from the location vowing to protect her. Both are shocked to find more hunters slain. This is when they confront the Onion Boss. Kishimoto and Kei flee with Kei leaving her due to the speed of the power suit he was wearing. She lucks out as the Onion Boss ignores her and continues in Kei's direction. She remains idle until the mission is suddenly over. Kishimoto returns to the room to face Kei and she is mad. Kei tries apologizing but Kishimoto brings up the absence of Masaru. She was not present to see him struck down by the Onion Boss to aid Kei. Kishimoto and Kei believe Masaru dead until another transportation brings Masaru back as well. The reunion is interrupted by the reading of points. Kishimoto is enraged by gaining her nickname "Titz" from Gantz. She also learns Kei was ogling her the entire time. The first mission was over and Kishimoto is allowed to go home.
Masaru and Kei see Kishimoto to her home by cab. She finally gives her name to the pair. Kei is shocked as they share the same first name. Kishimoto enters her home, returning to the bloody bathtub where it all should have ended. It isn’t long before there is a telephone ringing. Kishimoto answers to her frantic mother. She is mistaken as Shiori learns that the real Kei Kishimoto survived her suicide attempt. Kishimoto realized the words of Nishi were all true and that she now only exist as a copy of her former self. Kishimoto rushed to her room in tears in the presence of Shiori. She is quick to leave as Shiori learns of her sister's condition at the hospital while seeing Kishimoto before her eyes. Kishimoto seeks out Kei having his address book on hand from wearing his shirt. She remains on the streets after the mission. Kishimoto spends the following day making her way to Kei's home. He finds the exhausted girl at his doorstep and gladly allows her to stay with him. Kishimoto ends up prey to Kei's advances. It is not until confirming her meaninglessness as a copy that Kei backs off and tries to understand her situation. The next day brings new hope for Kishimoto. She decides to see her situation as a blessing. Kishimoto tells Kei of no longer being bound to the oppressing words of her mother and the shadow of a little sister. She is most joyous of finding true love as well in Masaru. The following day, Kishimoto and Kei are relaxing when both get a paralyzing feeling. Suddenly, Kishimoto and Kei find themselves back in Gantz's room.
Tanaka Alien Mission
Kishimoto is singled out by a new group of predators in the form of a biker gang. Masaru interrupts everyone to begin informing people about what was going to happen. Kishimoto is allowed to go change into her suit in the back room by herself. Butter the dog follows moments later. Masaru comes to check on Kishimoto to find Tetsuo spying on her while she changed. Kishimoto is horrified when Nishi kills one of the biker gang members over a matter of disrespect. Gantz reveals the target of the robotic Mr. Tanaka. The transfer begins and takes everyone but Kishimoto and Tetsuo. Once they are alone, Tetsuo tries to take advantage of the girl. Luckily, the transfer process separates the two. Kishimoto arrives to find Nishi fighting for his life against a Tanaka alien. She grows concerned when Masaru is the only one that goes to help. Later, when Nishi is dead, everyone regroups to discuss another player dying from having their head exploding. Kishimoto is the first to theorize that everyone may have bombs in their heads. Everyone spreads out to find the remaining aliens. She spends much of the mission trying to make sure Masaru isn't seriously hurt like in the first mission. Kishimoto is able to kill two of the Tanaka Alien while Kei ended up facing the boss. Once Kei is able to kill the boss (without a suit), the mission is over and the survivors return to the Gantz Room. Kishimoto receives 10 points and is aggravated that Gantz keeps referring to her as Titz.
After the mission is done, everyone is free to leave. Kishimoto tries to go home with Masaru instead of Kei. He reveals living with his aunt and didn't have a place of his own. This gets to Kei, who was hoping Kishimoto would be his girlfriend. He tries to look past it and Kishimoto goes home with him. She sleeps on the floor now and cant stop talking about Masaru. Kei ultimately loses it and Kishimoto decides it's best to leave. She spends the next couple of days on the streets. Kishimoto is asleep when she is transferred to Gantz for a new mission.
Buddha Alien Mission
Everyone looks at Kishimoto sleeping, when Butter decides to wake her up. She doesn't even acknowledge Kei and talks to Masaru. Kishimoto reveals originally wanting to be with Masaru after the first mission but only had Kei's information from the jacket he let her wear. Kei leaves to go cry in the back room. Kishimoto is allowed to go change in the back. She finds Kei involved with the new female Sei Sakuraoka. Gantz gives out the targets of the Grumpy and Angry Buddha Aliens. The mission begins and Kishimoto decides to help Masaru by explaining the weapons to everyone. Once the two giants Grumpy and Angry attack, Kishimoto spends a lot of time running around calling for Masaru. Kishimoto bares witness to Kei's new resolve to survive by any means. He ignores her now and cares only about killing the aliens. Kishimoto is among those that try to save an idle man that can't see the hunters or aliens. She helps everyone in suits battle the Super Buddha Alien, but Kei ultimately kills it. Everyone splits up to search for the boss to end the mission. Kishimoto and Masaru find Sadayo and Masanobu slain before the Kannon a.k.a One Thousand Arms Alien. Kishimoto notices the corpse nowhere near the statue but their bodies were separated from the waist down. Kannon tosses a liquid towards Masaru. Kishimoto, without hesitation, throws herself in front of him and suffers the same fate as Masanobu and Sadayo. Masaru is heartbroken and holds her tight until Kishimoto dies.
The Real Kei Kishimoto
Long after Copy Kishimoto had died in the Buddha Mission, Kei remembers the girl was only a copy. He goes to visit the real Kishimoto in hopes of starting fresh. Kei finds Kishimoto on her way home from school. They cross paths by chance, as Kei couldn't remember where she lived. He stumbles on his words to let Kishimoto know he likes her. She thinks he is just some weirdo planning to kill her. Kei doesn't help by revealing knowledge of her name without her telling him. Kishimoto is quick to leave, and Kei ends up crying again. Two years later, much has gone on in the world of Gantz. Kishimoto is in a subway, and crosses paths with Masaru. She is drawn to him, and wonders if he was thinking about asking her out.