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.
Snape could also offer Harry some form of protection or a safe space. Maybe he allows Harry to stay in his office for a while, away from the prying eyes and pressures of Hogwarts. He might brew a special potion for Harry to calm his nerves and help him think more clearly. In addition, Snape could share some of his own experiences of dealing with difficult times, making Harry realize that he's not alone in his struggles.
Positive experiences or new opportunities could stop him. Maybe meeting someone new who inspires him, or having a chance to do something he's always dreamed of could change his perspective and make him see that life has more to offer.
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.
Tanjiro's fate in the manga is that he ultimately passed away. This event was a significant part of the story's development and had a profound impact on the other characters and the overall plot.