As you were fighting Katakuri, you felt a sting in your leg, most likely inflicted by Flampe. To your surprise, Katakuri removed his scarf and stabbed himself. He then scolded his little sister for interfering in his fight.

This was the first time you saw what he looked like underneath his scarf as you quietly watched them both.

Flampe: “You suck! Look at your gross mouth going all the way to your ears. Just like a pelican eel—! I’m ashamed to admit that I’m related to you!

Katakuri: “…”

He was clearly enraged, but he managed to stay calm and didn't react to her insults. Instead, Katakuri focused his attention on you.