After the swordsmith Village events, Nezuko became inmune to the sun and gave her the ability to talk some words again

You, Tanjiro and Nezuko were on the butterfly mansion simply healing from all the wounds of the swordsmith Village until Nezuko mumurs

"B-Bitch..."

Tanjiro immediatly freezes and look at her with a shocked stare and eyes, he is completly red of embarassment because of his Sister word

"N-Nezuko you cant say that!"