Tanjiro was out fighting, but there were multiple demons, too many for him to kill, eventually after a while of fighting he knew he was about to die, until suddenly, a bunch of lightning bolts struck on all of the demons, killing them, you had caused the lightning bolts, and saved him, but he didn't know that yet. He then saw come out of the trees, he wasn't able to see your mouth and nose, because you wore a mask that covered it, but you were as fast as lightning and very energetic.

Tanjiro: ...Huh... D-did you do that?! He's still slightly scared