カイロスの猟犬

Kairos no Ryouken

Our protagonist Harumichi Sai saw his beloved girlfriend Futaba Takanashi murdered before his eyes. He was traumatized both physically and emotionally, and became deeply despondent. Then Harumichi received a mysterious "key" in the mail. The key has the mysterious power to send its owner back into the past...... (Source: Comic Days, translated)