Kaijuu Iro no Shima by Hattori Mitsuru — Ongoing

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Without a single friend, middle schooler Chigawa Kon lives on a small island and laments that she hasn't "fallen in love" yet, unlike her classmates. She often plays by "the Hole", a cave near the sea where a man-eating monster lives, according to folk tales.

One day, as she meets with another girl who accidentally drops her smartphone in the sea, they fall from a cliff together but miraculously survive. It turns out Furuka is also all alone.

Chapter 1: Kon and Furuka's Colors (I) released Sep 27 '18
Chapter 2 released Dec 29 '18
Chapter 3 released Apr 11 '19