There could be an alien with a plant - like appearance that can control nature on Earth in ways that the local supernatural beings can't. It comes to Earth because it senses the unique energy of the Highschool DxD world and wants to study it. Along the way, it gets involved in the various power struggles and forms an unexpected friendship with one of the main characters.
One idea could be an alien race coming to Kuoh Academy with unique powers that the devils, angels and fallen angels have to deal with. For example, an alien race that can manipulate time, causing chaos in battles and daily life.
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.
A futa version of Rias could be an interesting main character. She could have all of Rias's charm and leadership skills, but with the added element of her futa nature, which could lead to different power manifestations and relationship developments, especially with Issei.
The unique mix of supernatural elements in Highschool DxD fanfiction makes it stand out. You've got devils, angels, and other mythical creatures all interacting in a high school setting.
Well, in this kind of fanfiction, there are often powerful alien leaders who play important roles. They might be initially suspicious of the human but later come to respect them. There are also the alien scientists who study the adopted human, trying to understand human biology and culture. And don't forget the alien outcasts who find common ground with the adopted human. They bond over their shared feelings of not quite fitting in.
A new magical teacher could be added. This teacher could have a special connection to Kuroka, perhaps knowing about her past in ways others don't. They could guide her in her magical studies and also add some mystery to the story.
An exiled God. He was banished from his own pantheon for some misdeed. In the Highschool DxD world, he is trying to find a way to redeem himself. He has unique powers that are different from the other characters, and his story could be one of redemption and self - discovery as he interacts with the devils, angels, and fallen angels in the story.
One unique element could be the use of alien magic. For example, if the aliens have a different form of energy manipulation that the wizards in Harry Potter world don't understand. This could lead to a lot of interesting interactions and conflicts.
The Saiyans are quite popular. They are a well - known alien race from Dragon Ball, but in Naruto fanfiction, they can be re - imagined to fit into the Naruto universe. Their natural fighting abilities and the concept of power levels can add an exciting element to the story.
You can start by mixing different physical traits from various animals or alien concepts we already know. For example, an alien with the body of a mantis but the intelligence of a human. Also, give them unique personalities based on their species' culture. Maybe an alien from a water - based planet is very calm and collected because of their slow - paced environment.