As Yuuya surreptitiously observes his beloved Mariko, he's stupefied to witness a visage on her bare chest that seems to speak. Doubting his perception, he eavesdrops the next night but is caught in the act by Mariko. She reveals that the countenance belongs to her late homeroom instructor who suicided. Despite his fear, Yuuya's inquisitiveness urges him to delve deeper into this enigma.