A common theme is friendship. They are often depicted as becoming close friends and relying on each other in the Borderlands.
Another theme could be redemption. Maybe Chishiya has some past actions he's not proud of, and through his relationship with Arisu, he finds a way to redeem himself. Their bond can be the catalyst for personal growth for both of them, as they learn from each other's strengths and weaknesses.
One great source could be Archive of Our Own (AO3). There are numerous fanfics about Chishiya x Arisu there. You can filter by rating, length, and genre to find the ones that suit your taste.
The theme of survival in the Borderland also plays a big part. They are both trying to survive in this dangerous world, and their relationship can either be a hindrance or a help in that. In some fanfictions, they have to rely on each other despite their differences to make it through various deadly games.
Romance is also a big theme. Writers often explore the relationship between the reader and Chishiya, from the initial attraction to a deeper emotional connection. Some fanfictions focus on how they fall in love in the midst of the chaos of the Borderland.
One characteristic is that they often focus on Chishiya's intelligence. Writers like to show how he outsmarts others in various situations. For example, in many fanfics, he's the one who figures out the rules of the deadly games first.
One common theme is the exploration of their dark and complex relationship. Since both characters have deep psychological aspects, these fanfics often dig into how they interact on that level.
One common theme is adventure. Since the x company is likely involved in some sort of activity, fanfics often take the characters on new and exciting adventures. Another theme could be loyalty. Writers might explore how the characters in the x company show loyalty to each other or to their cause.
The theme of love against all odds is also quite prevalent. Given their different origins and the fact that Goku is already married in the original story, their relationship in fanfics has to overcome many obstacles. This could be social, moral or even physical (like dealing with other powerful characters who oppose their union), but they still find a way to be together, which makes for an interesting read.
One common theme is friendship. Scootaloo's relationships with other characters are often explored in terms of how they support and grow with each other. Another theme could be self - discovery. As Scootaloo is a young character, fanfics might show her learning more about herself.
Well, a very popular theme is the 'protective Jinyoung'. In these fanfics, Jinyoung is often portrayed as being very protective of the other character, whether it's a romantic partner or a friend. There's also the theme of 'pursuit of dreams' where Jinyoung and the other character support each other in achieving their goals. It's a way to show his positive influence in the story.
One common theme is her growth as a hero. Many fanfics focus on how Uraraka overcomes challenges to become a better hero, like improving her quirk control.