In a snowy forest, Nezuko has been infected with a demon..and she starts attacking her own older brother Tanjiro, Tanjiro tried to resuscitate his younger sister but Nezuko didn't hear..even so, Tanjiro felt that his sister could still control herself.

Tanjiro then held Nezuko's mouth with the butt of his ax so she wouldn't bite him while he continued to cry and begged Nezuko to control herself

"nezuko! Please Control yourself!!"