|Family|| Unnamed husband|
|First Apperance||Chapter 72|
"Hiroki... mom have something to said... I was... a bit unusual... I... was feeling killing was so great...... even mom myself can't control at all... At that day... compared to my family's death impact... the killing feeling was way stronger... I was... I was really surprised...... Sorry... I'm so sorry... I'm very sorry... mom is such a person like this..."
– Kotoko Tobe when she is nearly die, Chapter 130
Kotoko Tobe (斗部 コトコ, Tobe Kotoko) is a character introduced in third part of the story. She is one of the antagonists in third part of the story.
Kotoko was lived in a small house with her husband and her son Hiroki and they were live in happiness. Until one day, an thief come into Kotoko's house and killed her husband and son. Kotoko taking her kitchen knife to defend herself and kill the thief. After Kotoko killed the thief, she feel an very great feeling on killing, so she changed her original lifestyle to killing people.
After that incident, Kotoko keep continuously killing innocent people non-stop. Until Kotoko is finally catch by the police and sent into the Jail.
Chapter 71-185 (Third Season)Edit
Kotoko first appeared at Chapter 72, she is one of the 30 players to be chosen by Marble.
During the first trial, Kotoko suddenly meet Mizuki Kurashina. Mizuki states he knew about Kotoko due to one of his customer at his suicide website mentioned his family were killed by her, and they start fighting each other. When Kotoko asks why does Mizuki like Yuuma Mukai so much, he response is because Yuuma has changed his life from killing for the despair to killing for Yuuma, he also stated he is living for Yuuma and he would do anything for him, even if Yuuma wants to kill god. Soon, Mizuki saw Yuuma was beaten by Magura Aizawa which surprised him a bit.
After the first game finished, along with the rest of the players having bath at the hot spring. During the bath, Kotoko revealed her wish was releases her from jail, since after the trials is finished she will mostly back to the jail. Soon, along with the rest of female players was go outside the hot spring without wearing clothes, due to Paru-kun was "playing" together with the girls.
- Superhuman Speed - Kotoko can did a very fast moves with her attacks.
- Both Kotoko and Mizuki shared a lot of things similar. Both of them are living in their illusion world that need to killing people to achieve their goal. Both Kotoko and Mizuki's blood type is O.
- Kotoko's wish that want to be achieve by Marble is "Release from Jail".