It's never easy being the new kid, but imagine being a transfer student and joining the most cursed class in school! Originally from Tokyo, Kouichi moved to Yomiyama because his father's job sent him to India to conduct research. Since his mother died shortly after he was born, there was nowhere else for Kouichi to go but to live with his grandparents and aunt.
Unfortunately, Kouichi suffered from a collapsed lung before the school year began and he had to be hospitalized. While he was a patient, however, three of his future classmates came to visit him. Already awkward, the meeting turns strange when they begin asking him weird questions for seemingly no good reason. Kouchi's stay at the hospital becomes even stranger when he meets a girl with an eyepatch named Mei Misaki who's on her way to the morgue to visit her "other self."
By the time Kouichi is discharged from the hospital, school has already been in session for one month. Almost immediately, he notices that his class acts strangely. An aura of fear and trepidation radiates from his classmates, and he can't figure out why. He soon learns about the curse of class 3-3 that causes its students and their relatives to die in mysterious accidents. That's just an urban legend though, isn't it? It can't possibly be true.
His classmates, however, take the curse seriously. He learns that Mei is also in his class, except everyone else acts like she doesn't exist. This confuses Kouichi. Can't they see her? At first, he thinks Mei might be a ghost. Considering how scared his classmates are acting, it's not an unreasonable conclusion. Later, he discovers that Mei is alive and well. Their classmates are simply pretending not to see her.
As part of the curse on class 3-3, a dead person comes to join the living. It usually manifests as the incoming class discovering they have one extra student due to being one desk short. Unfortunately, Kouichi's class had the correct number of desks. To be safe, however, the class decided to follow the usual countermeasures put in place to minimize the number of deaths caused by the curse. The countermeasure? Act like one student is the extra and completely ignore their existence. In Kouichi's year, the extra is Mei.
But because no one explained to Kouichi how the countermeasures worked, he breaks the taboo and speaks to Mei. Even though his classmates are shocked by his behavior, no one will tell him why he needs to stop talking to her. Almost immediately, his classmates and their relatives begin to die, one by one. In an attempt to stop them, the rests of the class also begins to ignore Kouichi but this also fails.
As a result, Kouichi and his classmates start to work together to unravel the mystery of the curse and to find a way to stop it.
A strange girl with ghostly pale skin, Mei first met Kouichi in the hospital where he was a patient. But while he was there for a collapsed lung, she was there to deliver a doll to her dead cousin in the morgue—or so we think at first.
Mei lost her right eye to a disease when she was a child. Her mother, a dollmaker, replaces it with a glass eye, but instead of matching it to Mei's remaining eye, she makes it a different color because she thinks heterochromia is cool. Unfortunately, Mei doesn't share her mother's opinion and hates the glass eye so much, she covers it with an eyepatch. For unexplained reasons, Mei's glass eye has the supernatural ability to see what should remain unseen: she can see people who are close to death.
Unlike Kouichi, Mei is quiet and solitary. Combined with the paranoid aura of class 3-3, her personality and appearance lead Kouichi to assume she might be dead at first. In reality, Mei already suspects that the countermeasures have failed and that the curse had begun before Kouichi joined the class.
It turns out that Mei's mother is not actually her mother but her aunt. Mei's "mother" and her sister, Mei's true birth mother, were twins. While the sister gave birth to twin girls, Mei and Misaki, Mei's "mother" miscarried. The loss devastated her and since her sister's family was going through financial difficulties, they gave her Mei to help her cope with the grief. Mei was the one selected because her sister's name was Misaki and the name "Misaki Misaki" would have been awful. That's the reason why Mei already suspected the curse had been activated while Kouichi was still in the hospital. The person who died had not been her cousin but rather her twin sister. What made the situation more tragic is that Mei and Misaki had been meeting in secret, well-aware that they were actually twins and not cousins, but due to the fact that Mei had been raised as the dollmaker's daughter, she couldn't acknowledge the connection or show the depths of her grief. And because of this, she can't lift blame the class put on Kouichi.
Once their classmates begin to ignore Kouichi in a failed attempt to curb the curse's effects, Mei grows closer to the boy. But because Mei is able to see the color of death on people, she eventually figures out who the actual dead person is in class 3-3. She keeps it a secret though, because how would it change things?
However, that assumption is proven wrong when Kouichi and the others discover a cassette tape that offers a way to stop the curse: they must kill the dead person and send them back to the world of the dead. Even after learning this, Mei doesn't share the identity of the dead person. The reason is because Kouichi would regret the knowledge and she doesn't want to burden him with the truth. In fact, once the class trip to the mountain shrine turns murderous and tragic, she originally plans to dispose of the extra person herself but Kouichi finds her before she can.
The head of class 3-3 countermeasures, Izumi is responsible for making sure her classmates survive the school year with minimal casualties. She was one of the three students who visited Kouichi while he was in the hospital. Feeling a strange sense of déjà vu, Izumi asked Kouichi if he'd ever lived in Yomiyama before, to which he replied no. She ends up asking this multiple times throughout the series and even dreams of meeting the other boy.
Izumi was absent on the day Kouichi joined their class, an unfortunate incident that leads to him speaking to Mei, who everyone in the class is supposed to ignore. Irritated that so much went wrong on the one day she doesn't go to school, she tries to salvage the situation. It's her idea for the class to also ignore Kouichi once the deaths begin in earnest, but she abandons the plan when it becomes obvious it doesn't help.
Frustrated that her attempts to stop the curse aren't working, Izumi is also jealous that Kouichi clearly prefers Mei over her, a fact she finds unbearable because she thinks Mei doesn't show enough remorse for what's happening to class 3-3. As the student selected to be the extra person, Mei should have avoided Kouichi.
It's later revealed that Izumi and Kouichi met one and a half years before the start of the series. He'd come to Yomiyama from Tokyo and she was grieving the death of her older brother, a casualty of class 3-3's curse.
Izumi dies on the class trip.
An athletic boy with an energetic personality, Naoya befriends Kouichi on the other boy's first day of school. Unfortunately, he'd failed in his duties to class 3-3. He'd been the one who was asked to explain to Naoya the special circumstances of their class, but he couldn't do it. When Kouichi confronts him about this, Naoya tells him to ask him again the next month. He does it to put the other boy off, not realizing that Kouichi would remember and follow up.
Like all the students of Yomiyama North, Naoya knows about the curse of class 3-3 but he didn't want to believe it. Once his classmates start dying, however, he has no choice but to. Soon, he teams up with Kouichi to figure out how to stop the curse.
Naoya has a crush on Izumi, but the other girl ignores his feelings to his disappointment. When he learns how to stop the curse, he takes matters into his own hands with tragic consequences. Suspecting that Tomohiko, his close friend since childhood, might be the dead person, Naoya begins to interrogate him. When Tomohiko fails to answer the questions, they get into a fight and Naoya accidentally pushes him out a window. Panicked, Naoya finds Kouichi and together, they look for Tomohiko's body, only to discover it's gone.
Naoya's actions accidentally set off a chain of events where the classmates turn on each other and try to kill each other in the name of stopping the curse and saving the class.
A good friend of Naoya's, Yuuya is one of the students to welcome Kouichi on his first day of school. Liked by everyone around him, he's nonetheless made uneasy by Kouichi's actions and persistent attempts to acknowledge Mei's existence. Unfortunately, his friendship is not enough to explain to the other boy what's going on. He instead keeps silent and goes along with Izumi's suggestion to ignore Kouichi the same way they ignore Mei. That doesn't seem very friendly at all!
A senior member of the art club, Yuuya's creepy illustrations and paintings belie his sweet, innocent appearance. Because Mei is also a member of the art club, he uses his status to force the other students to isolate her as well, even though they're not members of class 3-3.
Yuuya seems to have a crush on Miss Mikami, class 3-3's assistant homeroom teacher. He's always concerned about her safety and during the beach trip, he makes sure to bring her some food. Even during the tragic class trip to the mountain shrine, his thoughts are filled with finding her amongst the chaos.
Yuuya is one of the students who know about the existence of the cassette tape that reveals how to stop the curse. Because Izumi found out about it, she forces Yuuya to play it for her. His actions result in multiple students discovering the method and taking matters into their own hands. Because of the high body count experienced by their class, everyone has grown increasingly paranoid and scared since they don't want to die. As a result, their efforts to kill the dead person lead to disaster.
The librarian of Yomiyama North Middle School, Chibiki was the homeroom teacher of class 3-3 in 1972 when the curse first took shape. During that year, a popular honor student named Misaki died. After his death, however, his class began acting weird. They continued to pretend he was alive and much to everyone's horror, he appears in the class photo even though it was taken after his death. To most people's eyes, the photographed Misaki looks a little strange, like he doesn't belong, but Mei can see the color of death on him. Beginning in 1973 and every year after that, the curse began and an extra dead person joins class 3-3, causing death to their classmates and their relatives.
Fearful for his life, Chibiki quit being a teacher but couldn't bear abandoning the school entirely. Instead, he remained at Yomiyama North Middle School as the librarian. Ever since, he has kept track of the calamities that have befallen class 3-3 throughout the years, recording the deaths of the students and their relatives. When both Kouichi and Mei are both ostracized by their classmates, they take refuge in the library where they look through the meticulous records that he's kept for any clues.
A serious man, he accompanies class 3-3 on their trip to the mountain shrine. However, he leaves partway through to take a student to the hospital because his asthma needed treatment. By the time he returns to the inn, chaos has broken out and the students of class 3-3 have begun attacking and attempting to kill each other.
Kouichi's aunt, Reiko lives with his grandparents in Yomiyama North. She is also the assistant homeroom teacher of class 3-3. As a result, she tells Kouichi to call her Miss Mikami at school and never Reiko. She wants to ensure that there's a clear separation between school and home. It seems like a sensible thing to do, so Kouichi goes along with it.
When class 3-3's homeroom teacher, Mr. Kubodera, kills himself in front of the class, she takes over his responsibilities. Reiko is also a survivor of class 3-3, but because the curse is in effect, cannot remember the details of her year. It's her year, in fact, that figured out how to stop the curse. The beach trip is in part a way to meet a former classmate of hers in the hopes that he can shed light on the situation. The cassette tape that Kouichi and the others find was recorded by him.
In reality, Reiko is the extra dead person of class 3-3. The reason why there were equal number of students and chairs at the start of the year is because the place that's short a desk is the faculty room. It makes even more sense because no other class has an assistant homeroom teacher. When Kouichi realizes his aunt is dead, he finally understands the strange things his grandparents' pet bird says: it's echoing the things his grandfather said in his grief. That's also how Kouichi and Izumi previously met—he'd come to Yomiyama North to attend Reiko's funeral.
When Mei realizes that Reiko is the dead person, the curse loses its effect upon her. She remembers that she witnessed Reiko's murder and had watched the woman's body be thrown into a river. Even though Mei intends to kill Reiko a second time in order to spare Kouichi, he finds her before she can do it and decides to do it himself.
After the curse is broken, no one remembers Reiko's second existence except for Kouichi and Mei.