Yes, there are likely some fanfictions out there that might include a kiss between Kai and Aichi. You can try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net.
One way is to show them outside of cardfights. Maybe they start hanging out more, like going to card shops together to look for new cards. They could talk about their lives, their dreams related to cardfighting. Also, if one of them gets into trouble, like Aichi being bullied by some other cardfighters, Kai could come to his rescue. This would strengthen their bond. Another aspect could be that they start training each other's decks, sharing their insights on different card combinations. Through these interactions, their relationship can grow in a more personal and friendly way.
I'm not entirely sure specifically what that particular 'Aichi Sendou Reverse Fanfic' is about as it could vary greatly. It might be a fan - created story that takes the character Aichi Sendou and puts a spin on his normal story, perhaps reversing his character development, relationships, or his role in the plot of the original work.
One prevalent theme is teamwork. In the Cardfight Vanguard world, they need to work together. Fanfics often highlight how well they cooperate, like in battles against tough opponents. Also, the theme of loyalty is often present. They are loyal to their team and to each other, and this loyalty is explored in various ways in the fanfics, for example, when facing difficult decisions that might test their loyalty.
Typically, in 'aichi and kourin lemon fanfic', there would be a focus on the relationship between Aichi and Kourin. The 'lemon' part might suggest some romantic or even slightly more passionate interactions between them.
Some of the best fanfics often have detailed character development and an engaging plot. Look for ones that really dig into the personalities of Count D Leon and Uke Leon. For example, a fanfic that shows how their relationship evolves over time, through different challenges and events. Maybe there's a fanfic where they have to team up against a common enemy and in the process, their bond deepens.
Adventure is also a theme. Fanfic writers like to send them on various adventures, whether it's searching for powerful cards or exploring new areas in the Vanguard universe. During these adventures, their relationship is put to the test and strengthened, and new aspects of their personalities are revealed.
One great 'aichi x kourin fanfic' could be 'Aichi and Kourin's Unseen Bond'. It focuses on their relationship development in a more subtle way, showing how they support each other during tough times in the cardfight world.
Growth is also a major theme. Aichi is often depicted as growing both as a cardfighter and as a person. For example, he might start out as a novice and through various challenges in the fanfic, become a much stronger and more confident player.
Well, it might be interesting because it allows fans to explore different scenarios and relationships involving the characters. Maybe it delves deeper into their personalities than the original source material.