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.
Well, it really depends on what genre you like in the 'paris x yumi fanfic'. If you enjoy adventure - themed ones, look for stories where Paris and Yumi go on some sort of journey together. Maybe in one story they are exploring an ancient castle in a fictional land. However, without more specific information, it's hard to point out particular good ones.
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.
Some Tumblr blogs also post or reblog yumi x ulrich fanfics. You can search for relevant tags like #yumi x ulrich fanfic or #yumi and ulrich. It might take a bit more effort to find exactly what you're looking for compared to the dedicated fanfic sites, but it can be a great source for unique and interesting stories.
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 popular yumi x ulrich fanfic is 'The Bond Between Them'. It focuses on their relationship development in a school setting. It's really interesting as it shows how they support each other through different challenges at school.
First, start with their existing personalities. Yumi is often serious and focused, while William can be a bit brash. Have them interact in situations that force them to understand each other better. For example, in a group mission on Lyoko, they might have different ideas on how to approach a problem. By working through these differences, their relationship can start to grow.
One idea could be a story where William, after being rescued from XANA's control, has trouble fitting back into normal life at Kadic. Yumi could be the one to help him through it, and during this process, they discover new feelings for each other. Maybe they have to face some remnants of XANA's influence together, which makes their bond stronger.
In these fanfics, Yumi and Ulrich's love can be depicted in different ways. It could be a slow - burn romance where they gradually realize their feelings. Maybe it starts with small gestures of kindness and protection towards each other during battles in Code Lyoko. Their different personalities, Yumi's strength and Ulrich's determination, can make for an interesting dynamic in the love story.
A great fanfic in this context often has well - developed characters. It should stay true to the personalities of Yumi and Ulrich as seen in the original series. For example, Yumi's strong - willed and independent nature and Ulrich's bravery should be reflected.