Demon Slayer: I Have Peerless Insight

[Action-packed power fantasy + System + heroines (Nezuko, Kanao, Shinobu Kocho, and others)]

Tang Yuan, a homebody, transmigrates into the world of Demon Slayer and gains incredible insight from the start. He thinks all he has to do is stay on the sidelines and follow Tanjiro through the story, but soon discovers that the story has already changed. Now he has to shoulder the burden of fighting demons himself.

Note: Canon pairings will be broken up, and every character will have a romantic storyline. There may also be some love triangles. The story will follow the original fairly closely up to Mount Fujikasane, but after that it will veer off in a different direction with some new elements, including additional details about the demons.

The story focuses on the Hashira, and every character will get their moment. Of course, the main perspective will remain on the protagonist.