The Executioner and Her Way of Life, Vol. 5 (manga) — Mato Sato

Menou and her allies succeed in executing the mastermind behind the drug monstrine, but now they must face their true enemy—one of the Four Major Human Errors who once destroyed the world, Pandæmonium. The little girl is the concept of Evil brought to life, and she can create countless monsters from her flesh, revive herself at will, and kill for mere entertainment. Against her overwhelming power, Menou is backed into a corner...but with the help of Akari and a certain Princess Knight, can she manage to turn the tables?