Another theme is growth. Fanfictions such as 'Growing Together' show how Ted and Rebecca help each other grow personally and professionally. They learn from each other's experiences and become better versions of themselves, which is really inspiring.
Another theme is personal growth. Both Ted and Rebecca have their own issues to deal with, and fanfictions often show how they grow as individuals while being part of each other's lives. For example, Ted's homesickness and Rebecca's past relationship traumas are often explored in relation to their relationship.
One great Ted Lasso and Rebecca fanfiction is 'The Unlikely Bond'. It beautifully explores their relationship development in a more in - depth way than the show sometimes allows. It has a really engaging plot that keeps you hooked from start to finish.
The allure lies in their dynamic. David is ambitious and wants to make a name for himself in Night City, while Rebecca is this feisty, loyal comrade. In fanfiction, they can be put in all sorts of scenarios. They might get caught up in a conspiracy that forces them to rely on each other even more than usual.
A theme that often pops up is redemption. Maybe Nathaniel has made mistakes in the past and through his relationship with Rebecca, he tries to redeem himself. And sometimes, the fanfictions explore the theme of family, how their families (or lack thereof in some cases) influence their relationship and how they build their own little 'family' unit together.
Their friends like Marshall and Lily could be important characters. Marshall might offer legal advice about the adoption process as he's a lawyer. Lily could be the one who gives them tips on taking care of a baby since she has experience with her own child.