One great place to find Kanda x Allen yaoi fanfiction could be Archive of Our Own (AO3). It has a large collection of fan - created works for D Gray - Man. Just search for the tags related to Kanda, Allen, and yaoi.
I really like 'The Unspoken Connection'. In this fanfic, the chemistry between Kanda and Allen is palpable. It starts with a simple mission they go on together and gradually builds up their relationship in a very believable way. It's a great read for fans of the pairing.
The appeal of Kanda x Allen yaoi fanfiction lies in the contrast between their characters. Kanda is often seen as more stoic and reserved, while Allen is more empathetic and outgoing. This contrast creates an interesting dynamic that writers can explore in romantic or emotional relationships.
The popularity lies in their contrasting personalities. Kanda is cold and stoic while Allen is warm and empathetic. This contrast creates a lot of potential for interesting relationship dynamics in fanfiction.
In D.Gray - Man fanfiction, Allen and Kanda often have a complex relationship. They are comrades in the fight against the Akuma, but their personalities clash. Kanda is hot - tempered and Allen is more gentle and kind - hearted. Their interactions range from bickering to grudging respect for each other's abilities.
One common theme is the exploration of their pasts. Both Allen and Kanda have troubled pasts that can be delved into in fanfiction. Another theme is their growth as characters, especially in relation to each other. For example, how they overcome their differences and become better comrades.
If they were trapped in a parallel dimension where only they exist and they have to find a way back. They would be completely dependent on each other. They might start to open up about their past traumas, like Allen's past with the 14th Noah and Kanda's past with Alma. Through sharing and relying on each other, their relationship could evolve into a deep and trusting friendship or something more.
One common theme is the exploration of their complex relationship. Given their different personalities in the original work, fanfictions often delve into how they might overcome their differences and develop deeper feelings for each other.
One interesting plot idea could be Allen and Kanda being forced to team up on a mission in a completely new and dangerous area. Maybe they have to deal with a powerful Akuma that has unique abilities they've never encountered before. This would force them to rely on each other's skills, with Allen's Innocence and Kanda's sword - fighting abilities working in tandem.
A great idea could be that Kanda is hurt in a magical experiment gone wrong in the Black Order. It was an attempt to enhance his anti - Akuma weapon, but something backfires. This would not only physically harm him but also make him question his role and place in the Order. He might start to doubt if all their efforts are really worth it.