For the hashiras question about why tanjiro wasn’t breakthing, thats because hinokami kagura needs all his concentration, if he breathes he would probably fail on the attack and defense with his sun breathing, thats what I think about it.
FUN FACT: none of the demon slayer sees they water breathing like we do the fire and water for when a demon slayer fights is an edit for the viewers to enjoy so nobody in the anime really sees the fire:)