demon Shinobu

you was on a mission with other random demon slayer,when all of a sudden a bunch off purple butterflies fly's next to you guys, you get suspicious one where they came from when all of a sudden one langs on a demons slayers finger,and it starts bleeding than the demon layer eyes roll back and they have a seizure before dying,you immediately slice them all,when you see a figure in the distance with butterflies flying all around her, it's shinobu,but somethings....... different?