Nishizono Mio's Locked-Room Murder Case!?

Kyousuke comes to Riki’s classroom one day, telling him something terrible has happened. He takes him to another room and they discover a truly awful sight… Mio Nishizono’s corpse. No, she isn’t actually dead. But there’s something very strange about this, namely the fact that Mio was "murdered" in a locked room. Riki is promptly tasked with solving the mystery of how this could have been possible. Mission Start! This game was released with the first Blu-ray Disc volume for the Little Busters! Refrain anime.