Naruto is a must - have as the main character. He'd be the one to inspire the other ninjas to keep fighting. Hinata might also be a main character. Her Byakugan could help in detecting the hidden movements of the aliens. Shikamaru, being a brilliant strategist, would be involved in devising plans to counter the alien attacks. And Rock Lee, with his amazing taijutsu skills, could engage in close - combat with the aliens when their technology fails them.
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.
There could be an alien race that has a very different ideology from the people of Remnant. For example, they believe in a survival - of - the - fittest concept at an extreme level. Their leader, who enforces this ideology and leads the invasion, would be the main antagonist. RWBY would have to oppose this leader's cruel ways and protect their own values.
In a Naruto alien invasion fanfiction, the plot could involve aliens arriving in the Naruto world seeking a powerful chakra source. They might start by attacking small villages to test the strength of the ninja. Naruto and his friends would then have to unite the ninja world, learn about the aliens' technology and weaknesses, and develop new jutsus to fight back. Maybe some aliens could have the ability to absorb chakra, which would pose a great threat.
It's hard to say without reading it. But it could be some heroic soldiers or a smart scientist.
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.
Obviously, Harry Potter himself would be one of the main heroes. His experience in fighting dark wizards would give him the courage and skills to face the aliens. Hermione Granger would also be a key hero. Her vast knowledge of magic would be crucial in coming up with strategies against the alien invaders.
In this 'naruto after pain invasion fanfiction', Naruto is central, of course. But characters like Jiraiya could be important even though he's dead. His teachings and memories could still influence Naruto's decisions. Iruka, Naruto's first teacher, might have a role in helping Naruto deal with his emotional state. Gaara, as Naruto's friend and the Kazekage, could come to Konoha to offer assistance and strengthen the bond between their two villages. And then there are the other members of Naruto's team, like Kiba and Shino, who could be involved in various tasks related to the post - Pain invasion situation in Konoha.
One main character could be a military general on Earth. He has extensive combat experience and is tasked with leading the defense against the Star Wars invaders. Another could be a young orphan who discovers he has an uncanny ability to interact with the Force, which makes him a key figure in the fight. And perhaps a Jedi who has been exiled to Earth long ago and now has to step up to help his new home planet.
One possible plot could be that aliens invade Hogwarts. They might be attracted by the powerful magic there. The students and teachers would have to put aside their differences within the wizarding world and unite against the alien threat. Harry Potter and his friends could use their knowledge of magic, like defensive spells, to fend off the aliens.
Temari and Kankuro, Gaara's siblings, would also be involved. Temari is skilled with her fan and Kankuro with his puppets. They would be fighting alongside Gaara and Naruto to protect their village from the Sand - Sound invasion.
Naruto is, of course, very memorable. His determination to protect the village against Pain is always a central and inspiring part of any such fanfiction.