A really interesting plot could be Erika and Kyoya starting a new business together as a married couple. They would face challenges like financial difficulties, competition, and differences in their business approaches, all while trying to keep their marriage strong. This would show their relationship in a different light, not just as a romantic couple but as partners in a more practical sense. There could be scenes of them brainstorming ideas, arguing over decisions, and then making up in a really sweet way. It would add a lot of depth to their relationship and make for an engaging fanfiction.
Perhaps a plot where they decide to move to a new place after getting married. They have to adjust to a new environment, make new friends, and maybe even face some local mysteries or problems. This could involve them learning more about each other, their strengths and weaknesses, as they navigate this new chapter of their lives together. It could also include some cute domestic scenes like decorating their new home and having their first dinner party as a married couple.