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.
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.
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.
Naruto's normally bright and positive personality might become more conflicted. Since Douma has a more complex and often morally ambiguous nature, Naruto would have to grapple with new emotions. He might become more reserved as he tries to figure out how to handle Douma's powers without losing his own identity.
First, study their characters well. Know Tanjiro's kind and determined nature, and Kanao's shy yet strong side. Then, think of a unique plot, like them teaming up to save a group of children from a new type of demon. Start with a strong opening that grabs the reader's attention.
You need some graphic design software like Adobe Photoshop or Illustrator. Learn their basic tools and functions for manipulating images and adding effects.
Editing comics can be tricky. You might want to start by scanning your hand-drawn pages. Use tools to clean up lines, add shading, and adjust the colors. Also, make sure the text is clear and legible.