Another Episode S / 0 - light novel by Yukito Ayatsuji

Summer, 1998. Mei Misaki, age fifteen, has gone with her family to their seaside vacation home. There she meets the ghost of Teruya Sakaki, her classmate from Yomiyama North Middle School Class 3-3 who, like Mei, witnessed the mysterious events that had transpired at the school. There begins an adventure of memory and mystery as they search for the ghost's body and his memories alike.