Kaijuu Iro no Shima

A middle school student named Kon Chigawa lives on a small island where she was born and has never left. She is isolated and has no romantic experiences. During an incident on a cliff, she meets Furuka, a girl from the city, and saves her after they fall into the ocean. After regaining consciousness, the two find themselves in front of a cave rumored to contain monsters, an area Kon frequently visits. Following this encounter, unusual events start occurring on the island.