Pupa

In Pupa, siblings Utsutsu and Yume Hasegawa have only each other after being abandoned by their abusive parents, and that dependence becomes the center of a nightmare when beautiful red butterflies begin appearing in their world. Their arrival signals the spread of a mysterious virus known as Pupa, a cannibalistic plague that twists the body as well as the bond between the two children. When Yume succumbs fully to the infection, she undergoes a grotesque metamorphosis into a monster driven by an insatiable hunger for flesh. Utsutsu is only partially affected, but the virus leaves him with remarkable regenerative powers and traps him between survival and helplessness. As the infection deepens, Utsutsu clings to the promise he made to himself years ago: he will always be there for his precious little sister. That promise becomes a grim burden, because protecting Yume now means surviving her attacks, hiding the truth of what she has become, and struggling to keep the danger from spreading further. Pupa follows a brother's desperate effort to save his sister while facing the price of that devotion in a world where love and horror can no longer be separated.