Go Away, Ultramarine by Akina Yanagi

7.20

An island in Japan is the site for the dumped and the refuse. Nanakusa and Yu who were childhood and school friends meet on this island that is called Kaiden, a scary name that only refers to things not normal or earthly. The reunited friends strike a bargain and are soon involved in cases most would not dare be involved in or become entangled in.