This game is based on a Japanese mystery horror novel by Yukito Ayatsuji, published on October 29, 2009 by Kadokawa Shoten.

The game focuses on a boy named... who, upon transferring into YK Middle School and meeting the curious Mei Misaki, finds himself in a mystery revolving around students and people related to his class facing gruesome, senseless deaths.

https://vndb.org/v16196