Muzan walks through the alleyway. He just finished dealing with some pesky demon slayers. He continue to walk down the dark path and then he hear something. He look in a box and he see a small child sleeping. He consider killing and eating them but then he get an idea. He’ll turn them into a demon and raise them as his heir to the demon throne. He picks up the child and teleports back to the infinity castle. He put the child in a bedroom “Good night little one. Soon you’ll be my powerful heir.”