Iruka Sensei could also be a prominent character. He was an important figure in Naruto's early life. In a second - chance story, he might play a role in guiding Naruto in new ways, or perhaps Naruto could use his second chance to repay Iruka's kindness in a more significant manner.
For Naruto side, Naruto himself is very likely. His determination and growth arc can be interestingly combined with DC elements. Also, Sasuke with his powerful Sharingan could have some cool interactions in the DC universe.
Sasuke would be a likely character. He already has a dark past and a tendency towards brooding and seeking power, which would fit well in a 'world of darkness' setting. Orochimaru is another one. His experiments and his general amorality make him a natural for a darker Naruto story. And of course, Madara Uchiha. His grand and often cruel plans for the ninja world would be further explored in a darker fanfiction.
Tony Stark could also be a key figure in some fanfics, even though he's no longer alive in the main MCU timeline. His intellect and previous experiences with multiversal - related events (like in Endgame) could be explored in the fanfic. Maybe the Avengers find a way to access his knowledge or even a version of him from another universe to help them out.
Steven is the core, and among the Gems, not only the Crystal Gems but also Bismuth could potentially be part of it. Bismuth has a strong personality and her own connection to Steven. She could bring a different kind of energy to the harem. Also, Connie could be involved in some way, perhaps as a rival or a friend who helps Steven navigate his relationships with the Gems. Her human perspective could add an interesting layer to the story.
Naruto is a very likely character. Given his rebellious nature and his history of being an outcast in some ways, it's easy to imagine a scenario where he gets caught up in something that lands him in prison. His determination to break free and his loyalty to his friends would make for an interesting story.
The Hokage, whether it's Tsunade or others, would also be main characters. Since Naruto's actions often have a big impact on the village leadership and vice versa. With a second chance, Naruto's interactions with the Hokage could lead to different policies and decisions for the Hidden Leaf Village, making the Hokage an important part of the story.
Natsu would be a likely candidate. He's always eager for a fight and his reactions to the intense battles in Death Battle would be interesting.
Rock Lee could be an interesting character in this kind of fanfiction. He could use the Ninja Wire in his taijutsu - based combat, adding an extra element of surprise. Gaara might also be a good choice. He could use the wire in combination with his sand, perhaps using it to control the movement of his sand in more precise ways. Hinata could use the wire to enhance her gentle fist style, allowing her to strike from a greater distance while still maintaining the chakra - flow - based attacks.
Sasuke is also very popular. Fans love to explore what would happen if he had a second chance to redeem himself or make different choices regarding his path of revenge. He has a complex character, and in these fanfictions, there are a lot of possibilities for his development.
The entire village of Konoha could be highly affected. Naruto, with his second chance, could bring about positive changes in the village much faster. For the younger generation like Shikamaru, Naruto's new approach might inspire them in different ways. And for the older generation, they might be forced to re - evaluate their views on Naruto and the future of the village if he starts making radical changes early on.