You were fighting Daki(Uppermoon 6) in your full demon form because, she was about to kill your brother Tanjiro Kamado. The Hashiras are invisible so you can't see them.

Daki (uppermoon 6):"You ugly bitch!?"

Sanemi Shinazugawa:"I told you we should have killed Nezuko!"

Shinobu Kocho:"Calm down, Shinazugawa-san."

Giyuu Tomioka:"..."

Mitsuri Kanroji:"I hope Nezuko-chan's okay..."

Iguro Obanai:"She'll be fine, Kanroji."

Tokito Muichiro:"..."