The father of Tanjiro in 'Blade of Ghost Annihilation' was a member of the Ghost Hunters called Daisuke. He had outstanding combat ability and keen insight. At the same time, he also had a unique thinking and judgment ability, which was called the "transparent realm".
Daisuke had reached this level because he was constantly growing in battle, accepting all kinds of challenges and training, and constantly learning all kinds of knowledge and skills. His combat skills and thinking ability had been greatly improved, allowing him to better deal with various situations and make the right decisions.
In addition, Daisuke also experienced many events and tests, such as a life-and-death struggle with ghosts, parting with relatives and friends, and a life-and-death struggle with enemies. These experiences not only made him stronger and braver, but also made him more mature and wise. That was why he was able to remain calm, decisive, and intelligent in the face of all kinds of difficulties and challenges. He became a solid backing and an important mentor for Tanjiro.
The Hashiras would likely show concern. Some, like Shinobu, would immediately start looking into possible medical solutions. Giyuu might be more reserved in his worry but would still keep a close eye on Tanjiro. The other demon slayers would also be affected. They look up to Tanjiro, so his sickness would lower the morale of the group. They would try to support each other while waiting for Tanjiro to recover.
Well, it can be considered a spoiler if you haven't reached that part of the story yet. But if you're okay with knowing some key details upfront, then maybe not.
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.
Well, through the Dance of the Fire God, Tanjiro's character develops in multiple ways. Firstly, his sense of purpose becomes even more defined. He realizes the importance of the dance not just for himself but for the whole world he's trying to protect from demons. His compassion grows as well. When using the dance, he might see the pain of the demons more clearly, which in turn makes him more empathetic. His leadership skills start to emerge too. Other demon slayers might look up to him when he showcases the power of the dance, and he has to take on more responsibilities. Also, his determination gets a huge boost. Each time he performs the dance, he is more determined to end the reign of demons.