One interesting 'demon slayer reaction fanfiction' could be about the characters' reactions to modern technology. For example, Tanjiro might be amazed by a smartphone and its functions. Another could be their reactions to different types of food from our world. They might find pizza or ice cream very strange but delicious.
First, know the characters well. Understand their personalities, like Tanjiro's kindness and determination. Then, think of an interesting situation for them to react to, such as meeting a powerful new demon. Keep their reactions in line with who they are. For example, Zenitsu would probably be scared at first but then find some courage.
The Demon Slayer anime is largely based on the manga, but there are inevitable adaptations. Some character expressions and fight sequences might be slightly different to enhance the visual impact in the anime.
It depends on personal preferences. Some people think the manga has more depth and detail, while others enjoy the animation and voice acting of the anime.
In general, the Demon Slayer anime is very faithful to the manga. Some minor changes are made to make the animation more fluid and engaging, but they don't change the core of the story or characters.
The Demon Slayer anime has adapted a good chunk of the manga. But keep in mind that the manga is quite extensive, and the anime might take some time to catch up completely. Also, sometimes the anime might make some changes or omissions to fit the medium.
The Demon Slayer anime covers a significant portion of the manga, but it doesn't reach the very end. It stops at a certain point, leaving room for continuation or exploration in future seasons.