Two Brand New Ideas

1. The first idea involves a brother-sister duo. On a summer break together, they fall for one another (this can be discussed how it happens, so we can set the tone of the story however we want, i.e. it can have power dynamics involved). Suddenly, though, their freedom has been taken away now that they are back in the same house with their parents. How do they sneak around their parents backs? What will they do next? Will they get caught, and what will happen if they do? Let's follow their journey as they sneak around mom/dad!
2. Instead of brother-sister we add 'step' for those who like it better that way. There is also the option of focusing on the summer break part of the story. Perhaps they are staying with an older cousin or some friends. No matter who it is, it is still people that they have to sneak around and ALL the same questions as before apply here just the same. 

3. The same kind of idea here applies; it is a boss and his employee sleeping together, but they cannot let anyone in the office know. As before, the same kinds of questions, like how do they sneak around, what will they do next, will they get caught, and what will happen when they do apply here. 

4. This could be partners doing the exact same thing around friends. All the same applies. 

So in this story, YC has been marked by her adventuring guild as someone who is allowed to be bred with. While this may initially look like a privilege, it turns out that this can happen to her at any point in time. She is given a new adventuring uniform and tasked with going out and serving as many people as she can. It might not make sense at first, but soon she will learn about her new job.