One plot idea could be that they have to team up to save their family from a new villain in town. Since they usually have their differences, at first they struggle to work together, but as the danger mounts, they start to understand each other better and combine their unique powers to defeat the foe.
Well, it could change things a great deal. Enid and Rad would be less likely to be caught in the middle of their disputes. Their parents would also be able to trust them more. For example, they might be given more responsibilities around the house or in the family business (if there is one in the fanfiction) because they are working together instead of against each other.
Well, it really depends on what you consider 'good'. Some people might like the ones that focus on the emotional relationship between TKO and KO, while others might prefer more action - packed stories. You should look for reviews or ratings on the fanfiction platforms to find something that suits your taste.
Archive of Our Own is a popular place to start. It has a large collection of fanfictions.
Another interesting angle is to create an alternate universe where the events of the main story take a different turn. Maybe Aqua doesn't become an idol but pursues acting in a different way, or Ruby has a different career path entirely. This can lead to a whole new set of interactions and storylines.
One plot idea could be that Raven discovers she's pregnant in a world full of chaos and has to find a safe place for her unborn child. Maybe she teams up with some unexpected allies who help her on this journey.
One plot idea could be that Hiccup forgets all about his dragon - training skills and his relationship with Toothless. So, he has to start from scratch, relearning how to communicate with Toothless. This would create a lot of humorous and touching moments as Toothless tries to remind Hiccup of their bond.
One plot idea could be that Sokka discovers his powers during a dangerous mission. Maybe he's able to control the elements like water, which would be a huge shock to everyone since he's not a waterbender. Another idea is that his powers are related to his strategic mind, like being able to see the future of battles briefly, allowing him to plan even better strategies. He could also have powers that are connected to his weapon skills, such as super - strength when wielding his boomerang or sword, making him an even more formidable fighter in the group.
Maybe in the fanfiction, Naruto gets the Rinnegan as a result of a genetic experiment gone wrong (but in a good way). His Uzumaki genes combined with some unknown factor from an enemy he defeated. With the Rinnegan, he could unlock new jutsu that blend his already powerful Rasengan and shadow clone techniques with the abilities of the Rinnegan, like the ability to control gravity.
One idea could be that Lucy discovers a new magical power within herself. Maybe she finds an ancient spellbook that unlocks a hidden potential related to her celestial spirit magic. For example, she could learn to combine the powers of multiple spirits in a new and unique way, making her attacks much more powerful.
Maybe they get caught while using magic in a way that's not allowed in the public eye. They then have to face the consequences from the Shadowhunter authorities, which could lead to a whole adventure of trying to prove their intentions were good. They also might have to face the reactions of their friends and family who might be worried or disappointed.