Well, he could use it to transform into different alien species and gain their powers. For example, he could turn into a strong and durable alien like Four Arms and be better at fighting Death Eaters. It would definitely change the whole dynamic of the wizarding world as his abilities would be a combination of magic and alien powers.
If Deku had a quirk in fanfiction, it would likely impact his character development. He might have become more powerful quicker or taken on different enemies. The story could become much more action-packed or focus on different themes.
It could make for a really exciting and unique story. Deku's growth and challenges would be measured in a more structured way, adding a new layer of excitement to his journey.
Sasuke. He already has powerful Sharingan abilities. With the Omnitrix, he could add alien powers to his already formidable skills. He could use the speed of an alien form to enhance his own movement speed during battles and combine it with his Chidori attacks for even more devastating strikes.
Well, for example, Natsu's fire - dragon slayer magic could potentially interact with a heat - based alien form from the Omnitrix. Maybe when he's in that form, his fire magic becomes even more intense or has a different quality to it. He could use his dragon slayer skills to control the heat in a more precise way than the alien form normally allows.
In some Omnitrix fanfiction, there are crossovers with other universes. For instance, a story where the Omnitrix wielder ends up in the Star Wars universe. They have to use their alien forms to survive in this new and very different environment, facing off against Sith Lords and using their powers in creative ways to interact with the Force.
One interesting concept could be how the Omnitrix interacts with the unique chakra system in Naruto. Maybe it could transform the user into Naruto characters with added alien abilities from the Omnitrix. For example, turning into Naruto with the powers of Heatblast, allowing for a super - charged Rasengan with fire - based attacks.
Another could be an OC with the Omnitrix getting stuck in a parallel universe where the rules of the Omnitrix are different. For example, instead of being able to transform into known aliens, the OC has to figure out how to use new and strange alien forms that are native to that universe. This could lead to all sorts of adventures as the OC tries to find a way back home.
One idea could be a story where the Omnitrix is fused with a Pokeball, allowing the protagonist to transform into a Pokemon and use its powers while also being able to capture other Pokemon in a unique way. Another could be a cross - over where characters from Ben 10 (where the Omnitrix is from) end up in the Pokemon world and have to use the Omnitrix to survive and understand the new environment. A third idea is a story where a Pokemon trainer discovers an ancient Omnitrix - like device that gives them the ability to transform into rare and powerful Pokemon forms that no one has ever seen before.