First, understand the character of Riki well. Know his backstory, his personality traits like his determination, his vulnerability, and his loyalty from the original AI no Kusabi. Then, create a unique situation for him. It could be a new adventure, a different relationship dynamic, or a personal crisis that he has to face. For example, you could put him in a situation where he has to make a difficult choice between his friends and his own beliefs.
Their relationship would likely become more intense. Iason would be more protective of Riki. Riki might become more dependent on Iason for emotional and physical support.
I'm not sure specifically as it could be a very niche fan - created story. It might be a fanfic that involves Riki from 'AI no Kusabi' in a situation where he is being punished in some way, perhaps related to the power dynamics and complex relationships within the story's setting.
A cool idea could be a time - travel fanfic. Riki and Rin find themselves sent back in time to when the Little Busters first formed. They have to deal with the knowledge they already have while trying not to disrupt the past too much.
There is indeed a good number of fanfictions about Riki and Iason's love. Fanfiction writers are drawn to their relationship because it has elements of passion, power dynamics, and a certain kind of forbidden love. These fanfictions can range from ones that closely follow the original tone and setting to those that take a more creative and alternative approach to their relationship.
The emotional depth in these fanfictions can be really engaging. Since Riki has his own insecurities and Rin has her own issues, fanfic authors can really dig deep into how they help each other grow. Some fanfics show Riki becoming more confident because of Rin's straightforwardness, and Rin learning to be more open because of Riki's gentle nature.
In some fanfictions, a plot twist could be that Riki loses his memory related to Rin. This creates a lot of angst and confusion. Rin has to work hard to make Riki remember their relationship, and during this process, they both grow and change in unexpected ways.
In many Little Busters fanfictions, Rin and Riki often have a very special relationship. Riki usually plays a role of support for Rin. He tries to understand her complex personality. For example, Rin's shy and sometimes wild nature is something Riki has to navigate through. Their relationship can be seen as a deep friendship with potential romantic undertones. Riki's patience and Rin's gradually opening up to him make their interactions in fanfictions really interesting.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, and there are likely to be quite a few iason x riki ones there. Just search for the tags related to them.
There's a fanfiction titled 'Journey Together'. In this story, the author takes the relationship of iason x riki to different levels. It shows their adventures side by side and how they face various challenges together. It's really interesting as it gives a fresh perspective on their bond.