In the manga, Tanjiro and Kanao don't end up getting married. The story focuses more on their battles and character development rather than romantic pairings.
I would recommend 'Douma's Secret Admirer'. In this fanfiction, the reader is a shy character who secretly admires Douma from afar. It's full of cute and endearing moments as the reader tries to get closer to Douma without being too obvious. It's a really heart - warming read.
Well, the plot could involve Naruto being reincarnated as Douma. He would have to deal with Douma's memories and powers. Naruto, having his own moral code, might struggle with the darker aspects of Douma's character. He could use his ninja skills to fight against the enemies that Douma had in his world, but in a more heroic way than Douma did. Maybe he'd form new alliances with the characters in Douma's world and bring a new perspective to the power dynamics there.
Common themes in douma x kotoha fanfic can include redemption. Maybe Douma has some past actions that he needs to make up for, and Kotoha plays a role in that process. Also, there is often a theme of self - discovery. As they interact more, they learn more about themselves through the eyes of the other. This can be a very interesting aspect to explore in these fanfics as it adds depth to both characters.
Fanfiction.net is also a classic site for finding 'Douma x Reader Fanfiction'. It has been around for a long time and has a vast amount of content. However, the search function might not be as advanced as AO3, but with a bit of patience and browsing, you can still find some excellent stories.
One great tanjiro and kanao fanfiction could be where they go on a journey together to find a rare herb for an ailing comrade. In this story, their relationship deepens as they face various obstacles in the forest.
Tanjiro and Kanao's love is a slow - burning and sweet one. They first meet as comrades in the fight against demons. Tanjiro's kind heart and strong will gradually draw Kanao out of her shell. Kanao, who was initially rather reserved, starts to open up more because of Tanjiro. Their relationship develops as they face numerous challenges together, and their mutual respect and growing affection for each other are heartwarming to watch in the series.