The fanfiction could start with Naruto somehow ending up in the world where Hellion Mercury and X - 23 are in trouble. He then uses his ninja skills, like stealth and his vast array of jutsu, to infiltrate the place where they are held captive. Naruto's ability to sense danger and his quick thinking would be essential. As he rescues them, they might start to learn from each other. Hellion Mercury and X - 23 could gain some new perspectives from Naruto's way of life, and Naruto could also learn about their powers and how to work together more effectively.
In this fanfiction, Naruto's values of friendship and protecting others would drive him to save Hellion Mercury and X - 23. He might face enemies that are new to him, but his combat experience would help. Naruto could use his Sage Mode to gain an edge in battle while trying to extract Hellion Mercury and X - 23 from a dangerous situation.
It could be that Naruto uses his speed and agility to reach Hellion Mercury and X - 23 in time. His chakra control would also be important, perhaps to heal any injuries they have. The fanfiction might show how Naruto adapts to their situation quickly and takes charge of the rescue operation.
In a fanfiction where Naruto saves Hellion Mercury and X - 23, it could be an amazing crossover. Naruto's heroic nature and powerful jutsu could be used to rescue them from various threats. Maybe they are in a world where different powers collide, and Naruto's skills are the key to their survival.
Another aspect could be a friendship story. Naruto, with his never - give - up attitude, might inspire Sailor Mercury to be more assertive in her battles. They could team up against a common enemy that is threatening both their worlds. This would bring out interesting character dynamics as they learn from each other's strengths.
A plot could involve Sailor Mercury getting lost in the Naruto universe. She'd have to adapt to the ninja lifestyle. Maybe she'd use her water - based powers in new and interesting ways, like creating ice - sculptures to distract enemies. Naruto could help her understand the ways of the ninja world, and they'd form a strong bond through these experiences.
It could change the power dynamics in the Hidden Leaf. With Kushina back, her knowledge of the Nine - Tails and her strong Uzumaki abilities could shift the balance. For example, if she rescues Naruto from a situation where the village was about to lose him, it would boost the morale of the villagers and ninjas. They would see that there is still hope with someone as powerful as Kushina around. It might also make other villages more cautious about attacking the Hidden Leaf, knowing that Kushina has returned.
One main theme is the combination of different powers. Naruto has his chakra - based ninja powers and Rory has her own combat skills. When they come together, it's about how these powers interact.
In a RWBY Mercury Redemption fanfiction, his relationships can play a crucial role in his development. If he forms strong bonds with the good guys, like befriending Jaune or Weiss, they can influence him to change. Their different values and outlooks on life can gradually rub off on him, shaping him into a better person.
Sasuke could be a likely candidate. Despite their differences, Sasuke and Naruto have a deep connection. He might hear about Naruto's capture and come to his rescue, driven by their past friendship and the rivalry that also binds them.
It could be other villages as well. Since Naruto has made friends and allies from different villages during his adventures. For example, the Sand Village might send some of their ninja to help, considering Naruto's relationship with Gaara.
His friends from Konoha like Shikamaru and Choji could help. Shikamaru is smart and can come up with great strategies, while Choji can provide brute strength in battles.
I'm not sure specifically about fanfiction with both 'x 23' and Hellion. You could try searching on major fanfiction platforms like Archive of Our Own. They have a large collection and you might be able to find something related by using the search filters.