In a crossover with 'The Matrix', Neo would be an interesting addition. He could use his skills in the virtual world to help Marty and Doc Brown understand and manipulate the digital aspects of time - travel technology that might be affected by the Matrix. His ability to see the code could potentially help them fix glitches in the DeLorean's time circuits.
In a crossover with 'Naruto', Naruto himself would be an interesting addition. His love for ramen could be a starting point. He could be amazed by Soma's cooking skills and end up challenging him to a friendly shokugeki. Another character could be Kakashi. His laid - back attitude yet sharp taste buds could add an interesting dynamic. He could be a tough judge in a shokugeki battle.
Zero would be an obvious and interesting character to include. His backstory and his relationship with X could add depth to the fanfic. Also, in a crossover, he could have some unique interactions with characters from other franchises.
Well, if you cross it with the Star Wars universe, Darth Vader could be an interesting addition. His dark power and combat skills would be a great contrast to the characters from Into the Badlands. It would be fascinating to see how they interact and whether they could form an alliance or end up as enemies.
One idea could be a crossover with 'Doctor Who'. The DeLorean could time - travel to a universe where the Doctor exists, and they team up to fix a time rift that's threatening both their timelines. Maybe Marty and the Doctor have to figure out how to combine the technology of the TARDIS and the DeLorean to set things right.
Luke Cage would also be a great addition. His unbreakable skin and street - smart attitude could bring a new dimension to the story. He could act as a moral compass for The Punisher at times, while also respecting his determination to clean up the streets.
A tough and experienced park ranger. They would have knowledge of handling dangerous animals and could be a key figure in trying to deal with the Indoraptor in a crossover situation. For instance, if the crossover is in a forest - like setting, the ranger could use their tracking skills.
Definitely Daredevil. As I mentioned before, their different moral compasses would create great tension. Elektra could also be included. She has a more ambiguous moral code and her skills would make her a formidable presence in a story with the Punisher.
Well, if it's crossed with a detective story like 'Sherlock Holmes', Sherlock himself could be a great addition. His deductive skills would contrast with the more action - based skills of the 'ansatsu kyoushitsu' characters. There could be a lot of interesting interactions as they try to solve mysteries together or perhaps be on opposing sides.
Harry Potter would also be a great addition. His knowledge of magic could be combined with the digital world of Summer Wars. He could use spells to protect the virtual world or help the characters understand new magical elements that might appear in the crossover. His loyalty to his friends and his courage would also be traits that would fit well with the Summer Wars characters.
A character like Alice from 'Alice in Wonderland' could be really interesting. She's used to strange and magical worlds, so she could interact with the Invisibles in a unique way. Maybe she could help Arthur navigate some of the more confusing aspects of the Invisibles' world with her own experiences in Wonderland.