Transformed into a demon and left mute, Nezuko travels with her older brother Tanjirou in a box on his back. She can change her size at will, and is a capable fighter when she needs to be, but has never killed or eaten any humans. Instead of gaining nourishment from humans, it seems that she recovers her energy by sleeping for long periods of times.
Eventually, it is discovered that Nezuko is not hurt by sunlight. At that time, she also has begun to be able to speak a little bit.