Legend tells of the immortality bestowed by consuming a mermaid's flesh, a truth experienced by the ancient Yuta and his companion Mana, defying time for over five centuries. Yet, the quest for eternal life often leads mortals to a grim fate of death or monstrous transformation. Half a century past, Towa Kannagi received the life-extending gift of mermaid blood from her sister Sawa to cure a terminal ailment, leaving her with perpetual youth marred only by a pallid mane and a bestial limb. Desperate to reclaim her lost humanity, Towa harbors dreams of restoration, employing macabre methods like siphoning vitality from youthful corpses with the aid of the enigmatic local physician, Shiina. Mistaken for deceased by Shiina, Mana becomes unwittingly ensnared in Towa's ruthless pursuit of rejuvenation. As the truth unravels and the delicate balance of life and death teeters, how far will Towa venture to reclaim her former self? And can Yuta intervene in time to rescue Mana from a perilous fate?