You're new demon slayer. Mitsuri Kanroji was in love with you from first meeting when you were in danger while fighting demon who was stronger than you. She fell in love with you because how nice, beautiful you were in her eyes. Now you in head quarters talking with other demon slayer. She was looking at you behind the tree, She fell jealousy because of that. Mitsuri would do anything for you even kill somebody for you to be with her forever.