High school student Kaname Sudou receives an invitation from a classmate to engage in Darwin’s Game, a mobile game unfamiliar to him. Despite his lack of knowledge about the game, when he activates the application, an unexpected green snake emerges from his phone screen, biting his neck and rendering him unconscious. Upon waking up in the infirmary without any visible signs of a snake bite, the school advises him to take the rest of the day off. Despite his confusion, he brushes off the bizarre incident as a hallucination and heads home by train.

However, curiosity gets the better of him, leading him to use the application once more. Initially relieved as the game seems like a typical battle game, Kaname’s contentment is short-lived. His in-game opponent suddenly materializes in front of him, wielding a knife and intent on hunting him down. Realizing that Darwin’s Game is not an ordinary pastime but rather a ruthless struggle for survival, Kaname frantically runs for his life.

In class 3-3 of Yomiyama North Junior High, transfer student Kouichi Sakakibara makes his return after taking a sick leave for the first month of school. Among his new classmates, he is inexplicably drawn toward Mei Misaki—a reserved girl with an eyepatch whom he met in the hospital during his absence. But none of his classmates acknowledge her existence; they warn him not to acquaint himself with things that do not exist. Against their words of caution, Kouichi befriends Mei—soon learning of the sinister truth behind his friends’ apprehension.

The ominous rumors revolve around a former student of the class 3-3. However, no one will share the full details of the grim event with Kouichi. Engrossed in the curse that plagues his class, Kouichi sets out to discover its connection to his new friend. As a series of tragedies arise around them, it is now up to Kouichi, Mei, and their classmates to unravel the eerie mystery—but doing so will come at a hefty price.

Nestled within a forest and sealed off by high gates, Grace Field House is home to a group of orphans who live together as a close-knit family under the care of their kind “Mama,” Isabella. While the children are required to take daily tests, they otherwise enjoy a carefree life, often playing outdoors, as long as they obey the strict rule of never straying beyond the orphanage grounds. From time to time, one of the children is adopted and leaves to join a new family, never to return.

Despite the peaceful appearance, the three eldest siblings begin to sense that something is terribly wrong. Their doubts soon lead them to uncover the horrifying truth behind life at Grace Field, as well as the dark secret hidden beneath the gentle smile of Isabella.