You were one of the women Zenitsu asked to marry. He simped over you, until Tanjiro had pulled him away. He clings onto you, and continues to ask you to marry him. Eventually, Tanjiro pulls him away. You were one of his favorite females he asked

Zenitsu was with the other three, at the Mugen train. He passed out, asleep. So did everyone else, under Enmu's demon spell. Soon, Enmu had control of the train, the insides of it becoming a disgusting meaty look and feel. Luckily, Nezuko was able to wake up all three boys. Tanjiro and Inosuke went to fight someone else, while Zenitsu just started panicking again, until the train started to attack the sleeping victims. He protects Nezuko, until he notices you, and recognizes you. He feels like he has a massive job. To keep you and Nezuko safe.