Who could be the main villain in a 'Naruto and Sailor Moon Reloaded Fanfiction'?

One possible interesting plot could be that Naruto and Sailor Moon somehow end up in the same dimension due to a strange magical rift. Naruto, with his ninja skills, and Sailor Moon, with her magical powers, have to team up to fight a new common enemy that is causing chaos in this merged world. They start off not understanding each other's abilities but gradually learn to combine their powers for greater effect.

A new character could be created as the main villain. This villain could be a powerful sorcerer who has studied the magics of both Sailor Moon and SVTFOE. He discovers a way to merge the two universes in a way that benefits him but is harmful to everyone else. He might try to control the Sailor Crystals and the magic of SVTFOE at the same time. To stop him, the characters from both universes would have to put aside their differences and fight together.

Obviously Sailor Moon herself. Her kind - hearted and brave nature would make her a great addition to the harem. And also Sakura from Naruto. She's strong - willed and has a long - standing relationship with Naruto that could develop further in this fanfiction.

Maybe a corrupted version of one of the Sailor Scouts. She could be jealous of Naruto's attention towards the other Scouts in the harem. So, she makes a deal with a dark force from Naruto's world, like a powerful Orochimaru - like character. This combined power of dark jutsu and a twisted Sailor power would create a very interesting and complex main antagonist for this crossover fanfiction.

The Dark King from Sailor Moon could team up with the Volturi. The Dark King's thirst for power combined with the Volturi's strict vampire laws could create a really menacing force. They could be trying to take over both the magical world of Sailor Moon and the vampire - filled Twilight world.

A corrupted spirit that was once a guardian of the Underworld but has been twisted by jealousy or a thirst for power. This spirit sees the Sailor Guardians as a threat to its newfound plans of domination. It uses its knowledge of both the Underworld and the weaknesses of the Sailor Guardians to try and defeat them. It might also try to turn some of the underworld creatures against the Sailor Guardians.

Perhaps in the fanfiction, Naruto and Sailor Moon are siblings in a world where both ninja and magical girl powers exist side by side. Naruto could teach Sailor Moon some of his combat techniques, like how to use a kunai effectively. In return, Sailor Moon could show Naruto the power of her transformation and how to use her tiara as a weapon. Their relationship could be centered around protecting their city or world from a common threat that combines the dark forces from both of their original stories.

One of the memorable villains from the Sailor Moon manga is Jadeite. He's often involved in schemes to undermine the Sailor Scouts and gain power for himself.

One possible plot could be that Naruto and his friends are transported to the Sailor Moon universe. Naruto's chakra could be seen as a similar power to the Sailor Scouts' magic. They could team up to fight a common enemy, like an evil force that is draining both the chakra and the magic energy in both universes. Naruto's determination and the Sailor Scouts' love and justice - driven powers could combine in unique ways to defeat the foe.

One interesting plot could be that the Sailor Guardians are on a mission to a world similar to Naruto's. There, they meet Naruto and his friends. Naruto is initially confused by their strange powers but quickly realizes they can help fight a common enemy. Maybe an evil force from the Sailor Moon universe has teamed up with Orochimaru. The Sailor Guardians' magic combined with Naruto's ninja skills could make for some epic battle scenes.