A new and original character could be the main villain. For example, a powerful shinobi from a far - off land who has heard of Konoha's power and wants to prove his own might by invading. This character could have unique abilities and a complex backstory that ties into his motives for the invasion.
It could be Orochimaru. He has always had an interest in Konoha and its secrets. Maybe he decides to launch a full - scale invasion this time to get his hands on something he desires.
Well, perhaps in this 'naruto invasion of konoha fanfiction', Naruto is actually being mind - controlled to lead the invasion himself. It would be a huge shock for his friends and allies when they find out. This could lead to a lot of internal conflict as they try to figure out how to stop him without hurting him.
Sakura could also be a main character. She's a strong ninja in her own right. In a fanfiction like this, she could be involved in treating the injured when the Hellsing - related chaos starts. Maybe she also tries to understand the unique physiology of Alucard. And Integra from Hellsing. As the head of the Hellsing organization, she could be the one trying to establish some sort of order between the two worlds.
It could be a corrupt elder in Konoha. They might be power - hungry and see Naruto as a threat to their control. So they manipulate the situation to make Naruto the enemy.
Maybe Danzo could be a major antagonist. He's always been a shadowy figure with his own agendas. He might see Naruto as a threat to his secret operations and influence in Konoha, and thus play a key role in getting Naruto executed.
Obviously, Naruto would be one of the main characters. His never - give - up attitude and powerful chakra would be crucial in fighting the aliens. Sasuke would also be important, with his Sharingan and combat skills. Sakura, with her medical ninjutsu, could play a big role in treating the injured ninjas during the invasion. Kakashi could lead the strategic planning, using his vast experience.
It could be a rogue ninja from within Konoha who has embraced the 'darkness' fully and wants to reshape the village according to his own twisted ideals.
The main antagonist could be a new character. For example, a powerful ninja from a rival village who has a vendetta against Konoha. This ninja could manipulate Naruto into leaving Konoha by spreading false rumors about the village. Then, he tries to use Naruto's power as an assassin for his own evil plans.
It could be a long - lost relative of one of the old villains like Orochimaru. Maybe this person has been in hiding, training and growing in power, and now wants to take revenge on Konoha for what happened to their family member.
Aside from Naruto and his immediate family, characters like Kakashi could also be important in this fanfiction. He was Naruto's mentor, and he would surely be there to welcome them back. And Sasuke might also play a role, as he is Naruto's friend and has a connection to the village too.
Maybe the main antagonist is a powerful figure within Konoha who doesn't want Naruto to leave and become an independent force. He secretly sends assassins after Naruto. When Temari gets involved, this figure also targets her. His actions are driven by his thirst for power and fear of Naruto's potential outside of Konoha's control.