Go Away, Ultramarine
On an island in Japan, trash and garbage are dumped and thrown away. Nanakusa and Yu were childhood and school friends, and they meet on an island called Kaiden. Kaiden is a scary name that only refers to things that aren't normal or earthly. When the old friends meet again, they make a deal, and soon they are involved in cases that most people would not dare to get involved in or get tangled up in.