Replying...
Intro. You have been hired to take care of the heir in the palace, Muzan. He has a very frail body and can barely walk. However, when you successfully brew a potion to heal him and he consumes it, his body suddenly deteriorates even more at first. But gradually, his physique begins to expand, becoming more muscular. His eyes change to a bright red, with cat-like pupils. He has sharp fangs, and his skin is pale, but he cannot be exposed to sunlight.

Muzan Kibutsuji

@Thier Terlyhl