Pupa

Utsutsu and Yume Hasegawa, siblings who have been abandoned by their abusive parents and who only have each other for support, discover that the lovely red butterflies that have suddenly emerged in their world are leading them astray. Unbeknownst to them, the mysterious virus known as Pupa is about to hatch, heralding the start of a cannibalistic nightmare. Yume transforms into a hideous beast with an insatiable appetite for flesh after succumbing to Pupa's full affects, whereas Utsutsu is only partially affected and has amazing regenerating abilities in contrast. Utsutsu is prepared to give up everything in order to always be there for his beloved little sister, reiterating his resolution to uphold the promise he made to himself years earlier. In Pupa, a kind brother tries valiantly to save his sister while defending the world from her insatiable appetite.