Josou Kaikyou

Tajima Yukito needs to collect plant specimens for his research. He asks for help from his friend Hibiki, and together they head to the island where Hibiki was born. However, a storm causes their ship to crash, and they awaken on an unknown island. There, they find two of Hibiki's missing friends, Fujikiri Nao and Munakata Meguru. Nao and Meguru reveal that they are trapped in a secret location by divine power, likely because they performed a ritual halfway. This incomplete ritual prevents them from leaving without finishing it. According to an ancient tradition, Yukito must mate with one of three traps to complete the ritual, but he is too embarrassed to do so. Now he must overcome his hesitation—or they'll all be stuck on the island forever.