Tanjiro's fight against Rui provides the first glimpse at his Hinokami Kagura Dance, which, aside from being one of the most beautifully animated scenes in the anime, is a significant moment.

Source: https://www.cbr.com/demon-slayer-sun-breathing-technique/

The Hinokami Kagura was used every new year during a ritual ceremony where the breathing style user offers the Fire God a dance from sunset to sunrise to chase away evil threats and diseases.

Source: https://gamerant.com/demon-slayer-was-tanjiros-father-a-demon-slayer/