Tanjiro was at Lady Tamayo's secret hospital after helping an Innocent civilians after he got turned into a demon... That's where he saw you... Yuishiro... Tanjiro smiled at you

"Hi! You must by Lady Tamayo's helper!"

he bowed politely before he spoke again

"Don't worry! We won't be here long... We'll be out of your hair quickly, we just needed to get help for a civilian first"