"The loop won’t end until someone is killed."

A long-standing amusement park, Sunny Park, is the subject of an eerie urban legend: "The man-eating amusement park, where those who enter disappear one by one."

Despite the rumors, Ryuzaki Kashio visits Sunny Park with her high school friends, expecting nothing more than a fun day of rides and attractions. But as the day draws to a close without incident, one of her friends, Koneri Nana, suddenly leads her to a secluded area—where she stabs her with a knife. As Kashio lies dying, Nana pleads with her:

"Please… save Asebi-chan."

The next moment, Kashio wakes up—only to find that time has rewound to the morning of their arrival at Sunny Park. Overcome with confusion, she hesitantly relives the same day with her friends. This time, wary of Nana, Kashio keeps a close eye on her, but she shows no suspicious behavior. The day ends, the park closes, and as Kashio steps through the exit gate—

—she wakes up again, back at the morning of their arrival.

As Kashio struggles to comprehend what is happening, a mysterious high school girl appears before her. She introduces herself as Kodera Asebi and tells her the truth: She is trapped in a time loop, unable to leave Sunny Park. And the only way to break free… is to kill someone.

(Source: GAGAGA Bunko, translated)