Who Turned Nezuko into a Demon

How did Nezuko become a demon?

Nezuko became a demon after Muzan Kibutsuji attacked her family. Demon blood entered a wound while she was still alive, so she became a demon instead of passing away from the injury. A strong will allowed Nezuko to resist demon temptations and not commit to hurting Tanjiro after being found.

Why did Muzan turn Nezuko into a demon?

Since he didn’t know anything about the Blue Spider Lily medicine, he needed others to find the plant for him by happenstance. This is the general reason why Muzan turned Nezuko into a demon. More specifically though, was the fact that Nezuko was of Kamado blood.