Demon Slayer: A Survival Guide for Demons

"Guess how long your little sister will live after you die?" Muzan wiped the blood from his fingertips and casually tossed the handkerchief into the muddy ground.

Watching the boy lying on the bed, struggling to breathe, Muzan pushed open the window. Beyond the bamboo grove, the moonlight was hazy.

"But if you become a demon, all these problems can be solved. What do you think, my Upper Rank?"