Well, in some fanfictions, Cedric might use his magical skills to shield Harry from physical attacks. For example, he could cast protective spells like Protego Maxima to create a strong shield around Harry when they are in danger. Maybe in a situation where dark wizards are attacking, Cedric steps in front of Harry and uses his wand to fend off the spells aimed at Harry.
Cedric could be developed further by showing his past. Maybe he had a difficult childhood that made him so eager to prove himself with magic. This could add depth to his character and make his actions more understandable. For example, if he was bullied as a child for not being good at magic initially, it would explain his constant need to show off his skills now.
The contrast between Hermione's studious nature and Cedric's more popular and athletic image makes for an interesting dynamic in fanfiction. Writers can play with this contrast, showing how they might initially clash but then find common ground. Maybe Cedric helps Hermione come out of her shell in social situations, while Hermione helps Cedric with his studies in a more complex area of magic.
A common theme is the development of their relationship. Since they have a unique dynamic in the original story, fanfiction often explores how that relationship grows and changes.
Well, one interesting aspect could be the unique character interpretations. In fanfics, authors often explore different sides of Lisa Lisa that might not be fully shown in the original work. It could also be interesting to see how the lemon aspect, which might imply some sort of romantic or spicy elements, is incorporated into the story in a creative way.
It's also possible that Lisa Davies is a transfer student from a different wizarding school. Her arrival at Hogwarts could stir up things as she brings with her different magical traditions and knowledge, which then affects the way the Hogwarts students view magic.