Who could be the main antagonist in a 'matatabi x naruto fanfic'?

It could be Orochimaru. He's always been interested in unique powers and abilities. The idea of X - 23's mutant abilities and Naruto's jinchuriki powers would be very appealing to him. He might try to capture them both to use in his experiments to gain ultimate power.

Maybe an evil sorcerer from a third, unknown dimension who sees the potential in both Naruto's chakra and Pneuma's power. He plans to steal their powers to become invincible. He starts by creating unrest in both their worlds, pitting their friends and allies against them. Naruto and Pneuma must figure out his true identity and stop him before he succeeds in his devious plan.

It could be an evil ninja who has somehow gained access to the technology from Neo's world and wants to use it to take over the Naruto world. He might be able to create clones using digital technology, making him a very difficult enemy to defeat.

It could be a rogue member of Kara who has their own agenda and doesn't agree with any form of alliance with Naruto or the Hidden Leaf. This character might try to undermine any cooperation between Naruto and the rest of Kara.

Madara Uchiha could be a great antagonist. He could have somehow gained the power to cross into the Bleach universe and is causing trouble there. Yoruichi and Naruto would have to put aside their differences and combine their skills to stop him. Madara's powerful jutsu and his desire for power would make him a formidable foe for the duo.

One idea could be a story where Naruto discovers an ancient power related to Matatabi. Maybe he has a vision in which Matatabi appears and guides him to a hidden place full of chakra. There, he learns new jutsu that are infused with Matatabi's unique energy. This could lead to him being able to fight stronger enemies and protect the Hidden Leaf better.

One possible plot could be that Naruto, while on a mission, encounters Yugito and they end up having to work together to deal with some sort of threat related to Matatabi. Along the way, they learn more about each other's abilities and form a strong bond.

Madara Uchiha could also be a great antagonist. He sees Velvet as a threat to his plans for the Naruto world. He might try to eliminate her because she could potentially disrupt his grand scheme of things, especially if she starts to gain influence among the ninja clans.

It could be a rogue ninja who has a vendetta against Naruto and sees Sister Lemon as an easy target to get to Naruto. This ninja might have some special powers that make him a formidable foe, like the ability to control shadows in a more sinister way than Naruto's shadow clone jutsu.

A powerful demon or dark spirit could be the main antagonist. This entity could be attracted to the combined power of Naruto and fem Apollo. It might seek to drain their powers to become even more powerful itself. For example, it could be a demon from Naruto's world that has somehow crossed over into Apollo's realm and is causing chaos there, targeting both Naruto and fem Apollo because they pose a threat to its plans.