Hairi Takahara never expected summer to feel like a dream. Sent to Torishirojima to sort through his late grandmother's belongings, he's met with endless sea, quiet nostalgia, and mysterious girls, each chasing something just out of reach. As he settles into island life, lost memories begin to surface and he finds what he never knew he'd lost.

Keisuke Takatou wakes up in a featureless white room, unaware of how and when he arrived. While exploring his whereabouts, he notices six familiar girls huddled around a large monitor—his childhood friend Kanae Hokari, the class president Miyakou Ando, his English teacher Natsuki Aoi, his junior Rika Makiba, and his classmates Rinne Byakuya and Nemu Manaka.

As they attempt to make sense of their current situation, a voice suddenly declares through the monitor, "The game will now begin." The rules of the game are simple yet brutal; assigned as the "unlocker," Keisuke must select one of the girls as his "keyhole" and violate her in a specific manner. Only after he does this for five rounds will the group be promised freedom to the outside world.

"Withdrawal from the game will result in death," announces the mysterious voice...