|“||...Why has it come to this?! I don't get it! I just don't understand! WHY CAN'T I TRUST HIM?! I CAN'T TRUST ANYONE ANYMORE!!||”|
—Mitsuki Yamamoto, Corpse Party: Book of Shadows (Episode #5; 『Shangri-La』)
Mitsuki Yamamoto (山本 美月 Yamamoto Mitsuki ) is a student of Byakudan Senior High School class 2-4, a victim trapped in the Heavenly Host Elementary School, and a minor character introduced in Corpse Party (PC).
Mitsuki is a teenage girl of average height and below average weight. She has desaturated turquoise eyes and medium short wavy grayish brown hair. She wears two pink hair accessories on both sides of her hair, and the Byakudan Senior High uniform, consisting of a white sailor fuku with a red bow, a viridian pleated skirt and collar, white crew-cut socks and brown shoes.
Mitsuki Yamamoto is a classmate of Yuuya Kizami and the secretary of Byakudan's student council. She has a strong mind, a tomboyish and a somewhat naïve personality. She is also quite strict and likes to keep things clean and organized. She has become a big sister-like presence in both her class and the student council. Due to her merciless attitude towards slovenly men she is called “Hellgirl Mitsuki” amongst the male first-graders. As she does the chores at home with her grandmother, she is a very good cook. Her usual severe attitude might be a reflection of her motherly instinct.
Mitsuki and her fellow co-head of the Student Council, Masato Fukoroi, endured too much of their surroundings, shortly after seeing Emi Urabe's corpse from an assault of a sledgehammer. She starts crying and longs for Kensuke Kurosaki. After realizing the hallway to the other wing has opened, Yoshikazu Yanagihori appears and hammers her fellow classmate. She runs for her life and trips. With a minor injury, she walks forward slowly, encountering Tokiko Tsuji.
Later, Satoshi Mochida and Yuka Mochida see Mitsuki running away. The two siblings catch up to her. However, she refuses to trust the two and pushes them out of her way and flees. After Yuka gets separated from Satoshi, she finds Sakutaro Morishige taking pictures of her corpse. Her body strangely disappears after Chapter 3.
Corpse Party: Book of Shadows
Episode #5; 『Shangri-La』
After waking up, Mitsuki meets Kensuke across a large hole at the school hall and they talk about being trapped in Heavenly Host before Kensuke leaves to find another way to reach her since he can't cross the gaping hole. Mitsuki meets with Masato after waiting for Kensuke for a long time. Together, they try to find Kensuke and the others. After exploring the school for a while, they encounter Sakutaro who is looking for Mayu Suzumoto, and decide to team up together looking for their friends. They then find Emi by the pool. However, she seems to have hit her breaking point and immediately flees from the group, causing Masato and Mitsuki to chase after her, leaving Sakutaro behind.
After finding Emi's corpse, she and Masato flee the scene, before Yoshikazu launches a surprise blow to Masato's head from behind. While Masato is getting killed by Yoshikazu, Mitsuki flees and mourns for Emi's and Masato's fate. She then runs into the art room, finding a chisel to be used as a weapon to defend herself. Shortly after leaving the room to find Kensuke, she meets Yuuya. Mitsuki then tells him what has happened to the others. Yuuya promises to protect her, letting her guard down, and takes the chisel away from her. He then tries to kill her with the knife he got from Kai Shimada, but Mitsuki dodges his attack. Yuuya tells her that he is the one who killed Masato after he survived Yoshikazu's hammer blows. Shocked about the revelation, she frantically runs away from Yuuya, vowing to not trust anybody she meets.
Later Mitsuki runs into Sakutaro once more on the stairs between the first and second floor in a state of panic and pushes him away, claiming he is far too calm around the corpses and therefore something is wrong with him before running away.
Yuuya captures her and starts killing her, wanting her to scream due to people only showing their real selves in the last moments of death. She refuses to give him this satisfaction, and dies quietly, the first one of Yuuya's victims to deny Yuuya of what he wanted in someone's death. She is brought up later by Yuuya as he is killing Tomohiro Ohkawa in Extra Chapter 14 that he along with her had some backbone and didn't give him the response he wanted.
Her dead body is found by Sakutaro during the chapter's closing phase.
Episode #7; 『Tooth』
Mitsuki appears shortly in Tohko Kirisaki's flashback, scolding Masato for forgetting cleaning duties, and forcing Kensuke to help them, much to his dismay.
Corpse Party: Blood Drive
At the end of the game, Mitsuki's existence is restored, along with everyone else who died in Heavenly Host.
EX CHAPTER 03『The Unconceding』
Mitsuki appears with Masato if Kai chooses to go to the student council room. She complains how the president of the rakugo-style comedy research club is slow in submitting his budget application. She then mentions that she can imagine Masato doing rakugo, and then says that she strikes him as a father figure, to his horror. However, she says he is only kidding, and sees him as a mature, responsible young man, to his relief.
At that moment, Kai Shimada barges in and asks Masato about what Yuuya doesn't like, so Masato mentions that he seemed unsettled at helping Kurosaki at his part-time job, which is at a horror themed shop. Mitsuki however, gets suspicious, and asks Kai about his motives. Masato tells her to calm down, and Kai agrees, saying that she'll get lines on her perfect forehead, but he does like the way she looks when she's angry. He then kisses Mitsuki on the cheek, and goes, leaving a raging Mitsuki and Masato.
- In Corpse Party (PC, PSP, iOS, 3DS), Mitsuki runs into Satoshi and Yuka but in Corpse Party: Book of Shadows she never does.
- Corpse Party: Blood Drive, if the player chooses to enter the Classroom instead of the Student Council Room, then Mitsuki is the only character from Byakudan Senior High School that never appears in that game in any way because she only appears if you chose to enter the Student Council Room.
- Mitsuki was reviled by Kensuke that she had a boyfriend who she broke up with for going out with 3 other girls.
- Mitsuki shares the same corpse sprite as another girl from her school.
- In the Book of shadows manga, her shirt is cut by Kizami, but in the game, it isn't.