Owaranai Fuyu, Kowareta Yume no Kuni

A long-standing amusement park called Sunny Park has become the center of an urban legend: people who step inside mysteriously vanish. Despite the rumors, high schooler Kashio Ryuzaki visits the park with his friends, expecting nothing more than a fun day of rides and attractions. However, his ordinary outing takes a deadly turn when his friend Nana Koneri leads him to a secluded area and suddenly stabs him with a knife. Just before he dies, she desperately pleads:

"Please... Save Asebi-chan."

The next moment, Kashio wakes up, only to find himself back at the morning of their arrival at Sunny Park. Shocked and unable to comprehend the situation, he relives the day, warily keeping an eye on Nana, who had stabbed him before. Yet this time, she shows no suspicious behavior, and the park closes without incident. But as soon as Kashio steps out of the exit gate, time rewinds again, throwing him back to the morning of their arrival.

As his confusion reaches its peak, a mysterious high school girl appears before him. She introduces herself as Asebi Kodera and tells him the horrifying truth: he is trapped in a time loop, unable to escape Sunny Park. And the only way to break free... is to kill someone.

(Source: Shogakukan, translated)