I think Superboy would be really interesting. In Young Justice, he's still finding his place and dealing with his Kryptonian powers. In the Injustice universe, he'd be faced with a very different version of Superman. He could be a bridge between the two worlds, trying to understand the darker side of power that the Injustice Superman has embraced while also holding onto his own ideals from Young Justice.
Artemis could also be a great focus. She has a complex backstory in Young Justice, and in the Injustice world, she could use her skills as an archer and her street - smart attitude to navigate the chaos. Maybe she'd be part of a resistance group in the Injustice world, using her stealth and combat abilities to take on the regime. And her relationships with the other Young Justice characters could add depth to the story as she tries to bring them into the fight against Injustice.
Definitely Batman. He's a central figure in both universes, but in different ways. In Young Justice, he's a mentor, while in Injustice, he's fighting against a corrupted Superman. In a fanfiction, seeing how he'd interact with the Young Justice team in the Injustice world would be fascinating. He could be guiding them, but also learning from their more idealistic views. And his detective skills would be crucial in uncovering the secrets behind the Injustice regime and finding a way to overthrow it.
It could be Robin. Since he has a connection to Batman like Red Hood, he might have a unique perspective. He could be the one trying to understand Red Hood's motives and trying to bridge the gap between Red Hood and the rest of Young Justice. Also, his own growth as a hero could be further developed through this encounter.
Miss Martian from Young Justice could be a great focus. Her powers of telepathy and shape - shifting make her a formidable opponent. Also, her experiences as a young hero trying to fit in and be accepted, especially when facing the more established Justice League, can lead to some really interesting character development and plot twists.
Violet and Artemis would be great together. Violet's shyness and her ability to turn invisible could contrast with Artemis's more outgoing and direct nature. They could learn from each other's fighting styles and how to deal with personal insecurities while on a mission. Maybe Artemis could help Violet be more confident in using her powers in front of others.
Definitely Kid Flash. He has a connection to both Young Justice and The Flash. His relationship with The Flash could be explored further, like how he feels about being in the shadow of the more famous speedster while also being a key member of Young Justice. And his powers could be a great asset in the crossover, as he can keep up with The Flash in terms of speed to a certain extent.
The interaction between Naruto and Miss Martian would be quite interesting. Miss Martian has her telepathic and shape - shifting abilities. Naruto, on the other hand, has his chakra - based powers. Miss Martian could be intrigued by Naruto's chakra system and Naruto could be amazed by her mental powers. Also, Naruto and Beast Boy could have some fun interactions. Beast Boy can transform into different animals, and Naruto might find that really cool and they could come up with some unique battle strategies together.
I think Nightwing would be the most interesting. He has this unique blend of skills and a different background compared to the more well - known Justice League members. His time as Robin and then his growth into Nightwing gives him a lot of depth to explore in the story.
Batman would be really interesting. He's a master detective and strategist. He would be the one to study the Predator's behavior and try to find its weaknesses. His lack of superpowers but high intelligence would make for an interesting dynamic against the technologically advanced and physically powerful Predator.
Superboy would be interesting as well. He's constantly trying to figure out his place in the world, and in a homefront fanfiction, he could be exploring his humanity further. He might get involved in community service activities to understand normal people better, which could lead to some really cool character development.
Definitely Superboy from Young Justice. His super strength would be crucial in direct confrontations with the Injustice League. Also, Lex Luthor from the Injustice League as he is a mastermind and his plans would drive much of the conflict.
Definitely Subaru from 'Re:Zero'. His 'Return by Death' ability makes him a really unique character. In a crossover, seeing how he interacts with the super - powered heroes of 'Young Justice' would be fascinating. Also, Robin from 'Young Justice' could be interesting. His detective skills and leadership could contrast well with Subaru's more impulsive and desperate style of dealing with situations.