Another theme could be family acceptance. Their families' reactions to their marriage and how they deal with any potential issues or misunderstandings related to family expectations.
Growth and self - discovery are other themes. The relationship between the two can be a catalyst for each character to learn more about themselves, as they interact and face different situations together in the fanfic stories.
One great place to start looking for Sachiko and Yumi married fanfiction is Archive of Our Own (AO3). It has a large collection of fan works. You can search for the relevant tags like 'Sachiko and Yumi' and'marriage' to find some interesting stories.
To find great 'yumi and sachiko' rated M fanfiction, start by exploring different fanfiction communities dedicated to their source material. Since it's rated M, it might contain more mature themes like deeper emotional exploration or more complex character interactions. You can also ask in relevant forums or groups if anyone has recommendations. However, keep in mind that different people have different ideas of what makes a good fanfiction, so it might take some time to find ones that really resonate with you.
Archive of Our Own is a great place to start looking for 'yumi and sachiko' rated M fanfiction. It has a large collection of fan works, and its tagging system makes it easier to search for specific types of stories. Another option could be FanFiction.net, though their rating system and content availability might vary. Also, some smaller, niche fanfiction communities related to the characters or the source material they come from might also have such works, but they could be harder to find.
One great place to start looking for Sachiko x Yumi fanfic is on fanfiction.net. There are often many different takes on their relationship in the fanfics there.
One common theme could be friendship. Paris and Yumi might be depicted as having a really strong bond in the fanfics. Another theme could be discovery, like they are discovering new things about each other or about a new place together.
One popular theme is their relationship development. Fans often like to explore how their feelings for each other might grow and change over time.
Love and relationship development are common. It often focuses on how the characters interact and grow closer in the context of marriage.
Family and legacy is also a common theme. Elsa's marriage may lead to starting a family, and this brings up questions about the future of her kingdom. Fanfictions might explore how she will pass on her powers, or what kind of rulers her children will be. It's about building a new family unit and how that impacts the existing family of the kingdom.
Love and support are common themes. Since they are married in these fanfictions, they often show how they are there for each other through thick and thin. For example, when one has a problem at work or with friends, the other offers comfort and solutions.