After leaving his island home for Tokyo following his parents' passing, Shinpei Ajiro returns when tragedy strikes—Ushio, one of the Kofune family's daughters, drowns trying to save a child. Upon discovering suspicious marks on Ushio's body at the funeral, Shinpei suspects foul play. As he investigates, eerie events unfold, prompting Mio to recall a local legend about malevolent beings known as 'Shadows.' These Shadows are believed to herald doom for those who encounter them. Amidst the island's darkness, Shinpei confronts his destiny to honor Ushio's final wish: safeguarding Mio from the looming threats.