Momo and Mineta. This would be a comical yet also character - building pair. Momo is very proper and intelligent, while Mineta is, well, Mineta. Being cuffed together would force Mineta to be on his best behavior and Momo would have to deal with his antics, but they could also learn from each other in terms of using their quirks in different situations.
All Might and Shigaraki. It would be really interesting to see the symbol of peace cuffed to the main villain's apprentice. All Might could try to influence Shigaraki and show him a different path, while Shigaraki would be in a position where he has to face the hero he's been taught to hate up close.
Maybe it's a hero and a villain who get cuffed together accidentally. This could lead to some interesting character development as they start to understand each other's motives. For instance, if Todoroki was cuffed to a minor villain. Todoroki might learn more about the reasons some people turn to villainy while the villain could see that heroes aren't all bad.
Another possible theme is self - discovery. The characters may learn new things about themselves or each other while being in this unique 'cuffed together' situation. It could force them to confront their fears, weaknesses, or hidden strengths, and this journey of self - discovery can be a central part of the fanfiction.
One idea could be that two rival Pokemon trainers are cuffed together by a mischievous Pokemon. They have to learn to work together to escape and in the process, they discover new things about each other's training styles. For example, one trainer might be more focused on attack power while the other on defense. Through this forced cooperation, they might even combine their strategies to create a new and powerful way of battling.
I'm not sure about specific 'little witch academia cuffed together fanfiction'. But you can try searching on fanfiction websites like Archive of Our Own. There are likely to be some interesting works there.
One such visual novel could be 'The Captive Hearts'. In this story, the main characters find themselves cuffed together due to a mysterious circumstance.
A new trainer and a legendary Pokemon. Imagine a young trainer who accidentally cuffs themselves to a powerful and mysterious legendary Pokemon. The trainer has to figure out how to communicate with the Pokemon and gain its trust while they are literally bound together. This would be a great opportunity for character growth for both the trainer and the Pokemon.
Since I don't know this visual novel well, I can't say for sure who the main characters are. But usually, in a story about being 'cuffed together', there might be characters who are polar opposites, like a criminal and a detective who end up cuffed for some strange reason.
One great fanfiction with Aang and Katara cuffed together could be one where they are in a situation forced by some villains. They have to rely on their unique bending abilities and their strong bond. For example, Aang's airbending could be used to try and break the cuffs or at least make it difficult for the captors to move them around easily. Katara's waterbending could also come in handy for various things like creating distractions or even trying to freeze the cuffs. There are often fanfictions that explore their relationship deeper in such a situation, with them having heart - to - heart conversations while trying to escape.
One possible plot could be that the Powerpuff Girls Z are cuffed together by some villain's new device. They have to work together in a more restricted way to fight crime. Maybe they struggle at first with the lack of individual movement but then learn to combine their powers even more effectively in this new situation.