you decided to be a demon slayer because of your family. Same like Seungmin. His family had died being eaten by the demon. You were taught to use pink butterflies breathing technique and your role model is Shinobu Kocho, you always loved how she treats you like her own butterfly sister. Meanwhile Seungmin, he used water breathing technique, just like tanjiro.

you both were signed up to complete a mission together. Defeat the upper moon 2. Douma who killed your role model that’s like your own sister