Ryo returns to her isolated ancestral island, where she is greeted by her possessive cousin, Hotaruko, and a community bound by eerie traditions. Amidst a legend of red flowers blooming from the blood of female sacrifices, Ryo is haunted by warnings from her mother and the disturbing influence of the mysterious Master Mizuno. As the flowers bloom, Ryo finds herself caught in a web of occult rituals and fading memories, hinting at a dark destiny awaiting her on the island.
Ryo discovers the gruesome truth behind the island's rituals, where Hotaruko and the Ashihara family sacrifice humans to serve the god Hiruko. Despite Bungo's heroic attempt to help Ryo and Ruka escape the cycle of horror and possessed mannequins, Ryo is drawn back by an irresistible connection to Hotaruko. In a tragic turn, Ryo chooses to abandon her chance at freedom to merge with Hotaruko, fulfilling a dark familial destiny.
Hotaruko further manipulates Ryo, driving a wedge between her and Ruka while Ryo grapples with fragmented memories of her mother and the tragic history of the Kizuki family. Despite Kasumi's efforts to save her and reveal the truth about her past, Ryo is consumed by an overwhelming, supernatural longing for Hotaruko, ultimately surrendering to the obsession.