Kaijuu-iro no Shima  

かいじゅう色の島, Kaijuu Iro no Shima, Kaiju Island, 괴수 색의 섬, 怪异海岛, Monster-Colored Island

Kon Chigawa, a middle schooler living on a small island without any friends, feels lonely as she hasn't experienced falling in love like her classmates. She often plays near "The Hole," a cave by the sea where a monster lives according to folklore. One day, while meeting with Furuka who accidentally dropped her smartphone into the sea, they both fall off a cliff but survive miraculously. It turns out that Furuka is also alone.