Maybe there will be a group of magical creatures that are neither good nor bad. They are neutral but are crucial to the new trials. They can communicate with Sakura in a unique way, like through dreams, and they hold the key to unlocking some of the new Clow Cards' powers.
A new girl character might be introduced. She could be a former Cardcaptor who lost her powers and is now trying to regain them. She has a lot of knowledge about the Clow Cards that Sakura doesn't know, and she becomes a mentor - like figure to Sakura in some ways.
There could be a new character who is a mysterious wizard from another dimension. He comes to help Sakura in her trials, but his motives are not entirely clear at first. He has his own set of magical powers that are different from Sakura's, like being able to transform into different animals.
One idea could be that Sakura discovers a new set of Clow Cards with powers she's never seen before. For example, cards that can manipulate time in different ways like freezing time in a small area or making time move faster for a specific object.
Maybe a mysterious ninja from a hidden clan shows up. This ninja is intrigued by Naruto's situation of being left behind by Sakura and decides to help him. They could have some really cool powers like the ability to manipulate shadows in a different way than the Nara clan. Also, there could be a healer from a neighboring village who comes to Konoha. She helps Naruto deal with his emotional wounds from being left behind, and in the process, they become good friends.
It's hard to say for sure. But perhaps there could be ninjas from a far - off land that we haven't known about before.
For 'the new sith wars fanfiction', a character like Lyra, a Force - sensitive orphan who was raised by smugglers. She has a natural affinity for the light side of the Force but has a wild and unruly streak. Another potential character is Darth Malice, a new Sith Lord who is extremely cruel and has a vendetta against a particular Jedi family. His actions could drive much of the conflict in the fanfiction.
There could be a new rival for Ash. This rival might have a very different approach to Pokemon training, like focusing more on the beauty and grace of Pokemon rather than just battle strength.
A wise old owl could be a new character. This owl could be the one who actually has knowledge about the real threats (or lack thereof) in their world. Maybe he tries to guide Chicken Little and the other animals. Another potential character could be a mischievous squirrel. The squirrel could be constantly causing small troubles that make Chicken Little think the sky is falling all over again. For example, it could knock down acorns that make loud noises.
A wise old sea turtle could be a new character. He could be the one who gives the mermaid advice about the human world and warns her of the potential dangers.
There could be a strict Roman professor who is very traditional and gives Percy and Annabeth a hard time in their classes. This professor might not trust the Greek demigods at first and constantly tests them. Another potential character could be a Roman demigod who becomes their friend. This demigod could introduce them to all the cool spots in New Rome and help them understand the Roman way of life better.
There might be new characters who are the masters of certain types of magic or skills that haven't been shown much in the story yet. For example, a character who can control time in a very different way from what we've seen before. Or perhaps a character who is a master of illusions and uses that to deceive both enemies and allies. There could also be new characters who are related to the antagonists in some way, like a henchman with a special power that makes him a tough opponent.
It's hard to say exactly. But maybe there will be some foreign soldiers from lands outside the walls that we haven't seen before. They could bring new fighting styles and different perspectives on the Titan problem.