One characteristic could be the exploration of their relationship, whether it's a deep friendship or a more complex dynamic. Another might be the use of the unique settings or story elements from the original source material that features these characters.
I'm not sure which specific 'ein x aaron fanfic' you might like. You could try searching on popular fanfiction websites like Archive of Our Own. They have a wide variety of fanfics, and you might be able to find some great ones there.
Overcoming obstacles is also quite prevalent. It could be external factors like enemies or internal ones like their own insecurities. For instance, in many fanfics, they have to deal with people who don't approve of their relationship, be it as friends or something more. And this makes for an interesting plot as they fight against such odds.
One great 'Ninjago Jay x Zane Fanfiction' is 'Electric and Ice'. It beautifully explores their friendship evolving into something more. The author does a wonderful job of portraying Jay's energetic nature against Zane's calm demeanor, and how they complement each other. It has some really sweet moments that make you root for their relationship.
One common theme is the idea of redemption. Zane often has a bit of a troubled past in the series, and in fanfics, his relationship with Aphmau can be a path towards redemption. Another theme is the discovery of love. They might start off as just friends or even enemies, and then gradually realize their feelings for each other.
A strong plot is another characteristic. It could be an adventure that the two embark on together, or a story about how they overcome differences. In some cases, it might be a mystery that they solve side by side. The plot should be engaging and keep the reader interested.
Another theme could be friendship. Before a romantic relationship, they might be friends first, and fanfics could show how their friendship evolves over time. Also, there could be themes related to self - discovery. As they interact, both Zane and Kawaii Chan might learn more about themselves and their feelings towards each other in the fanfics. It's also possible that some fanfics might have a theme of adventure where they go on adventures together, which in turn strengthens their relationship.
One popular kai x zane fanfiction is 'The Bond Between Them'. It delves into their unique friendship within the context of their shared adventures. The story shows how they support each other through tough times and grow together as characters.
There's also 'Laurence and Zane: A New Chapter' which is quite good. It delves deep into their personalities and how they interact in different situations. It shows their growth as individuals while also exploring their relationship. For example, there are parts where they have to overcome misunderstandings, which is really interesting to read.