Romance is a very common theme. Given their relationship in the original work, many fanfics explore the romantic aspect between them more deeply, like how they handle their feelings for each other.
One great source could be fanfiction.net. They have a wide variety of fanfics on this pairing. You can search by the characters' names and sort through the results to find ones that seem interesting.
For Naruto, you can focus on his growth in a new context with Medaka. Show how his ninja values interact with Medaka's way of thinking. For example, his loyalty and friendship concepts might be different from hers. As for Medaka, explore how she adapts to Naruto's world of ninjas, like learning about chakra and jutsu.
I'm not entirely sure specifically what'medaka all fiction' is about without more context. It could potentially be a collection of fictional works related to something named Medaka, perhaps a character, a place, or a specific genre within the Medaka universe.
Searching for a very specific fanfic like one about Zenkichi Medaka being pregnant can be a bit of a challenge. Fanfic writers often come up with all sorts of creative ideas, but not all of them are easy to find. You could start by looking at the most popular fanfic websites dedicated to the source material that Zenkichi Medaka is from. Check the tags and search functions carefully, and you might get lucky and find what you're looking for.