One popular overpowered Izuku fanfiction is 'One for All: Unlimited'. In this, Izuku has an extreme version of One for All that gives him near - godlike powers right from the start. He's able to take on villains with ease that would normally be a huge threat in the canon story.
In some overpowered fanfiction, a character could have the ability to instantly copy and enhance any quirk they come across. So if they see someone with a strength - based quirk, they can not only copy it but make it much stronger. This would lead to some epic battles and power - growth storylines.
Some fanfictions make Izuku overpowered by enhancing the nature of One for All itself. Maybe it gives him unlimited stamina or the ability to share his power with others in a much more efficient way. This changes the power dynamic and makes him far more powerful than in the original story. He could then train a group of heroes to have similar levels of power, making him a key figure in a new kind of hero society.
Well, it really depends on the specific fanfiction. Some fanfictions do make Ichigo overpowered. They might do this to explore different storylines or just for the fun of it. For example, in some, he could have a sudden boost in his reiatsu that makes him almost unbeatable. But not all fanfictions take this route. There are also those that focus on his character development in a more realistic way within the context of the Bleach universe and don't make him overly powerful.
Maybe it has the ability to absorb chakra. So when Naruto is in a fight against an opponent with a large amount of chakra, he can use the sword to drain some of that chakra, weakening the enemy while strengthening himself. The sword could then store that chakra for later use, like to boost Naruto's own attacks.
It could be a sword that can cut through any substance, like the Susanoo easily. Just imagine Naruto swinging it and slicing through powerful jutsu defenses as if they were paper.
Goku would probably be the most overpowered. His ability to constantly increase his power level and his wide range of energy attacks like the Kamehameha would make him a tough opponent in Super Smash Bros. He can also fly, which gives him an advantage in the game's arenas.
First, you need to know the characters well. For example, understand their existing powers in the original 'Code Lyoko' series. Then, think about how you can enhance those powers in an interesting way. Maybe give Aelita the ability to create multiple towers instead of just one at a time.
It can expand the lore. For example, if a fanfiction gives a character an overpowered quirk, it might make readers think about how such a quirk could exist in the original My Hero Academia world. It could inspire new ideas about the origin of quirks or how society would adapt to such powerful abilities.
People who enjoy action - packed and power - based stories would like to read it. Those who are into stories with unique abilities and how they are used in different situations.