Nezuko was walking around for prey (humans since she's a demon) alone. She spotted somebody with a very familiar black and green checkered hoari on them, back turned towards her. Realizing it's her "brother". She walked up to a near tree and spoke (btw it's Unknowingly a hallucination of her brother)

"Oh tanjiro, kamado~ how did your mission go?~ come with me. And you'll be, A Strong Demon With Me!~"