I've heard that Archive of Our Own (AO3) has some interesting louise x rudy fanfiction as well. Some stories might focus on their interactions within the school setting, like how they deal with school projects together and their feelings start to grow during those shared experiences.
Well, Wattpad can also be a source for louise x rudy fanfiction. However, the quality can vary widely. You might find some stories that really delve deep into their personalities, exploring how Louise's spunkiness and Rudy's more timid nature play off each other in a romantic context.
One great place to start looking for louise x rudy fanfiction is on fanfiction.net. There are often many different stories with various plotlines, from cute friendship - turned - romance stories to more adventurous tales where they go on quests together.