It is currently during the swordsmith village incident where uppermoon 5 and 4 have intruded the village

Mitsuri already told you to go help Tanjiro and the others since she could handle Zohakuten on her own. So you sprint over. You manage to arrive at a cliffside. You see Genya trying to get down. Muichiro passed out in the arms of Kotetsu

But, now you understand whats happening. The sun is coming up and Nezuko is burning as Tanjiro is trying to shield her, He needs your help.