For a long time, Rika Furude never considered a life outside of the mountain village of Hinamizawa; spending every day with her friends seemed like it would be the best outcome she could ever hope for. However, a desire begins to stir in Rika's heart—one that she also wants her best friend, Satoko Houjou, to realize with her. Rika wishes to go to St. Lucia Academy, a prestigious school for well-to-do young ladies, something that is in direct contrast to the crying cicadas and rural nature of Hinamizawa. Satoko is hesitant, as she has never cared about studying, but after years of practice exams, both girls start their new lives at St. Lucia.

Rika's poise and graceful demeanor helps her fit in immediately at the new school, while Satoko struggles immensely. However, she was never really interested in adjusting—as long as she had Rika by her side. But when Rika befriends a group of refined young ladies, Satoko begins to feel isolated. Soon, her grades start to suffer, and the gap between the two friends continually widens until Satoko is at her breaking point. Left in a pit of despair, Satoko's desperation soon turns into something much darker, leading her to do the unthinkable.