One great 'Muichiro x Reader' fanfiction is 'A Meeting in the Mist'. It beautifully captures Muichiro's somewhat aloof nature while gradually developing a sweet relationship with the reader. The descriptive language used really makes you feel like you're in the Demon Slayer world with them.
One common theme is the deep emotional bond between them. Given their relationship in the original work, fanfictions often explore how they support and care for each other on a more profound level. Another theme could be adventure, where they go on quests together and their relationship develops during those experiences.
The relationship development between Muichiro and the reader has to be believable. It can't be too rushed. A slow - burn, where they gradually get to know each other, understand each other's quirks, and form a deep connection over time is much more appealing. Also, the setting should be in line with the Demon Slayer universe. Whether it's in the Demon Slayer Corps headquarters or on a mission, the details of the world should be well - described.
A great one is 'When Demons Meet Heroes'. This fanfic explores how the characters from 'kny' would fare in the world of 'bnha' and vice versa. It has some really cool fight scenes where the skills and quirks from both sides are pitted against each other. It also delves into how the two different cultures in the shows would interact.
One idea could be to have characters from Boku no Hero Academia (bnha) and Demon Slayer (kny) participate in a joint training session. For example, Deku from bnha could learn some swordsmanship techniques from Tanjiro of kny. This would create an interesting dynamic as they come from different worlds with different power systems.
You can try fanfiction websites like Archive of Our Own (AO3). There are often a large number of fanfictions about various pairings, including muichiro x yuichiro. Another option is FanFiction.net, but the content quality may vary. You can also check out some dedicated anime or manga fan communities where fans might share their own written fanfictions or recommend good ones.
Another way is to check out fanfic communities on Reddit. There are subreddits dedicated to both 'Demon Slayer' and 'My Hero Academia' where people might share or recommend 'kny x bnha' fanfics. You can also post a request for such fanfics there and the community might be able to help.
Definitely not. Genya remains outside the ranks of Hashira throughout the manga. This is because of a combination of factors such as his skills, experiences, and the overall direction of the story.