Well, it's hard to say exactly. Maybe Shepard from Mass Effect would find it really strange. Since the two universes are so different in terms of story, characters, and technology. They might be confused by the Halo 4 fan - made stories that don't fit their own universe's logic.
One possible reaction in a fanfiction could be about the new dragon species introduced. A character might be in awe, thinking 'These dragons are so unique! Their colors and abilities are like nothing I've ever seen in Berk.'
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.
A common reaction in fanfiction about Dragon Ball Super Broly is shock at his raw power. Many fans write about how other characters, like Goku and Vegeta, react when they first see Broly's incredible strength. For example, Goku might be excited to face such a powerful opponent, seeing it as a new challenge in his quest for greater strength.
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.