Nightwing is a great choice. He has a strong connection to Batman as his former sidekick. In an Injustice fanfiction, Nightwing could be the voice of reason when Batman starts to go too far in his fight against Superman. Their relationship, with all its history and baggage, can add a lot of depth to the story.
Harley Quinn can also be an interesting pairing. She's a character with a complex past and unpredictable nature. In the Injustice universe, she could be either an ally or an enemy to Batman, depending on the situation. Maybe she has some inside knowledge of Superman's regime that Batman needs, but she'll only give it to him if he helps her with something first.
The Flash would be another good character to pair with Batman. His super - speed can complement Batman's detective skills. In a fanfiction, they could team up to carry out a heist on one of Superman's strongholds. The Flash could use his speed to get in and out quickly, while Batman plans the entire operation and provides the necessary gadgets and strategies.
Robin could be a great addition. He could act as a bridge between Starfire's more light - hearted nature and Batman's seriousness. His acrobatic skills and detective training could complement both of them in a fight. Another good character would be Nightwing. He has a connection to Batman already and his charm could add an interesting element when interacting with Starfire.
Batman himself is obviously very popular. He's the central figure and fans love to explore different aspects of his character in this 'injustice for all' scenario. His intelligence, combat skills, and unwavering sense of justice are always interesting to write about.
Obviously, Batman and Superman are the most prominent. Their complex relationship, which is a mix of friendship, rivalry, and ideological differences, makes them central to any fanfiction in this universe. However, characters like Wonder Woman also often play important roles. In some fanfictions, she may be caught in the middle of the Batman - Superman conflict, trying to mediate or having her own stance on the events that unfold.
One unusual character to pair with reincarnated Batman could be Doctor Strange. Their different worlds of magic and crime - fighting in Gotham could create an interesting dynamic. Another would be Groot. The contrast between the talking tree and the dark, brooding Batman would be really cool. And then there's Harley Quinn from a different universe where she's a hero. Her chaotic energy combined with the reincarnated Batman's new perspective could make for a great story.
Chat Noir would be a great pairing. Their different powers and personalities could create some really fun and exciting interactions. Chat Noir's flirty nature combined with Multimouse's more cautious approach would make for an interesting dynamic.
Goku is a great character to pair with Beerus. Their relationship in the original series is full of tension and mutual respect. In fanfiction, they could have all sorts of adventures together, like exploring new galaxies or training in unique ways.
Chloe could be a great addition. She could be a supportive friend who helps Clana in their relationship, or there could be some friendly jealousy triangle situations that add drama. Another good character to pair with them could be Lex. His complex relationship with both Clark and Lana in the original show can be further explored in fanfiction, like how he might try to break them up or use their relationship for his own gain.
Catwoman could also be paired with Batgirl in fanfiction. They have an interesting dynamic as Catwoman is more of an anti - hero while Batgirl is a full - fledged hero. Their encounters could range from tense stand - offs to unexpected alliances as they both navigate the seedy underbelly of Gotham.
Characters like Naruto from the Naruto series could be an interesting pairing. Naruto's positive attitude and his own powerful jutsu could be a contrast to Berserker's darker nature. Also, Captain America from the Marvel Universe would be a good match. Cap's leadership and moral compass against Berserker's more chaotic nature would create an interesting conflict. And for a more fantasy - based pairing, Legolas from The Lord of the Rings. His archery skills and elven grace against Berserker's brute strength would be a great visual and story - wise combination.
I think Mario and Hinata would be an interesting pair. Hinata's shy but strong - willed nature could contrast with Mario's always - positive and heroic attitude. And Mario could help Hinata become more confident in this cross - over scenario. Another good pair could be Toad and Shikamaru. Toad's small but brave self and Shikamaru's intelligence would make for an engaging dynamic.