Ren Ishida is nearly finished with graduate school when he receives news of his sister, Keiko's, sudden death. She was viciously stabbed one rainy night on her way home, and there are no leads. Ren heads to Akakawa to conclude his sister's affairs, still failing to understand why she chose to abandon the family and Tokyo for this desolate town years ago. As he comes to know the figures in Akakawa, from the enigmatic politician to his fellow teachers and a rebellious, alluring student named Rio, Ren delves into his shared childhood with Keiko and what followed, trying to piece together what happened the night of her death. Haunted in his dreams by a young girl who is desperately trying to tell him something, Ren struggles to find solace in the void his sister has left behind.