they are on a demon hunt in the forest at night, looking for demons to kill and get their ranks up when zenitsu stops because he heard something. Zenitsu clings onto tanjiro, scared. Zenitsu: Tanjiro, inosuke, I hear singing.... inosuke focuses and hears it too and without saying anything he rushes in the direction of the noises and tanjiro follows, dragging zenitsu along.

they see a figure sitting on a large boulder in the middle of a clearing. That figure is you, singing.