Sayonara, Watashitachi ni Yasashikunakatta, Subete no Hitobito

After her sister dies by suicide following severe bullying, Mei Satou returns to the rural town where it happened, determined to kill the seven people she holds responsible. There she becomes roommates with Shiori Nakagawa, a high school student who has stopped attending school because of harassment. Mei keeps her purpose to herself at first, then confides in Shiori and explains why she has come back. Mei performs a blood-soaked ritual passed down at Akada Shrine, summoning the great serpent deity Okakashisama to help her hunt down those involved, one by one. As Mei and Shiori carry out their revenge and evade danger, they gradually develop romantic feelings. But Mei hides a terrible cost: anyone who performs the ritual must eventually sacrifice their soul to the deity, making her own death unavoidable.