Tanjiro might use his sense of smell to detect hidden threats. Since his sense of smell is super - enhanced, he could sniff out any demons or traps in the way of saving Rengoku. For example, if there are demons disguised as allies, Tanjiro would be able to tell by their scent.
One possible plot twist could be that Tanjiro has to sacrifice a part of his own power to save Rengoku. Maybe he has to give up some of his newly acquired breathing techniques which he has worked so hard to master. This would show his selfless nature and his deep respect for Rengoku.
Definitely not. Genya remains outside the ranks of Hashira throughout the manga. This is because of a combination of factors such as his skills, experiences, and the overall direction of the story.
Well, the circumstances of Genya's death in the manga are quite complex. It involves a series of events and confrontations with powerful enemies. But I can't recall all the details at the moment.
Yes, in some fanfictions, Tanjiro is depicted as the reincarnation of Yoriichi. This concept adds an interesting layer to the story as Yoriichi was an extremely powerful and legendary figure in the original lore. The idea allows for new storylines where Tanjiro might inherit some of Yoriichi's skills or have a deeper connection to the past events related to Yoriichi.