Dissolving Classroom (溶解教室, Youkai Kyoushitsu, also translated as "Supernatural Classroom") is a story released by Ito in March 2013. It is the first chapter of the Youkai (Dissolving) Series.
A new student called Yuma Azeri has transferred to Keiko's school. Azeri repeatedly, profusely apologizes to everybody around him, and is soon targeted by bullies. Meanwhile, reports have emerged of the outbreak of a mysterious disease. One day, as Keiko's walking home, she notices a creepy little girl who has been following Keiko for some time. Keiko runs but the girl catches up to her every time. The girl's tongue grows to an unnatural length and she says that she wants to suck out Keiko's brain. Keiko runs out into the road and is hit by a truck.
While Keiko is in hospital, Azeri comes to the hospital and apologizes to her and her parents. He explains that the girl is his sister, Chizumi; whom he has raised alone since their parents died. Azeri began torturing animals as a way to cope with his abusive parents, and he killed a snake; after this, Chizumi's personality became warped, and he believes she's cursed by the snake. He visits Keiko in hospital every day and she begins to fall in love with him.
Chizumi begins to torment women around the neighborhood and Azeri always apologizes to them. One day Keiko goes with him and finds that when she kneels to apologize with him, she feels better. She decides she wants to be Chizumi's friend and teach her to open up to others. Azeri refuses to invite Keiko to his house and says that she doesn't understand how evil Chizumi is. Keiko knows where Azeri lives so she goes over there anyway.
Keiko enters the house and is attacked by Chizumi, who wants to suck out Keiko's brain. Chizumi says that her brother did kill a snake, but this was part of a ritual to summon a demon. By apologizing and placing his hands together, he activates a bond with the demon, which grants Azeri powers. Keiko doesn't believe this so Chizumi opens a cupboard to reveal the severed heads of the Azeri parents. Their brains had begun to liquefy and leak out through their eyes and noses.
When Keiko gets home, her parents are lethargic and confused, and have thick mucus dripping from their noses. She thinks it's flu and soon starts to feel unwell like them. When she gets to school the next day, everyone has the mysterious flu. Keiko again intervenes to stop Azeri being bullied but then sees that their classmates' brains are leaking out through their eyes and noses. They collapse dead on the floor. Chizumi arrives and begins to lick up the melted brains. She says that when Azeri apologizes to someone, the demon makes that person's brain melt. Azeri denies this and claims that his parents were killed in an accident, but Chizumi ate their brains and became evil.
Azeri chases Keiko through the school, screaming that he's sorry. He puts his hands together and the demon appears behind him. Keiko discovers that everyone in the school has died from their brain melting. She goes to hospital where the doctors do their best to save her, but her parents have died and Keiko will die soon too. No one discovers where Yuma and Chizumi Azeri went to, but Keiko is convinced they'll do the same thing in another town.