There could be a situation where a biker was in a crowded area, like a biker rally. There was some sort of misunderstanding or rivalry. Maybe one biker thought the other was disrespecting him or his group. Tensions built up, and instead of using fists, one biker impulsively headbutted the other. However, to really know the full story, we need more details such as the location, the people involved, and what led up to that very moment.
I'm not sure specifically which "motorcycle headbutt" story you are referring to. There could be various incidents involving motorcycles and headbutts in different contexts, like in a motorcycle race where a rider might accidentally collide and there could be a headbutt - like impact. Without more details, it's hard to tell the full story.
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.
It's a fake story. Often in the world of information, there are false tales spread for different motives. It could be for getting attention, or perhaps as part of a prank. Since it's specified as a 'fake story', we can assume there's no real - world incident of a girl actually getting headbutt in the face. It's important to be critical of such stories and not believe everything we hear or read without proper verification.
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.