On a day like any other, Shouta Amano plans to confess his feelings to his crush, Koharu Saeki. However, he receives a strange text about something called the "Friends-Eater Game," informing him that he has a "healthy status" and that his antidote is someone's fingers.

He assumes it is just a prank, but later discovers that his entire class received the same message, including Koharu. Later, Koharu calls him to the roof, and she reveals that her message was a bit different than the rest: she has an "infected status"—and her antidote is Shouta's fingers. The two of them brush off this strange development, and Shouta uses the moment to confess to her... only to have her die brutally in front of him a few seconds later.

Realizing that Koharu's death was caused by not heeding the orders of the message, Shouta and his classmates must play the Friends-Eater Game and follow every horrifying command within the time limit, or face a gruesome death.