If Naruto saves Mikasa, he might also introduce her to his friends back in Konoha through some sort of communication jutsu. His friends could offer their advice on how to deal with the Titans. Meanwhile, Mikasa could share her knowledge of combat strategies with Naruto and his friends. This exchange could lead to new ways of fighting for both Naruto's world and Mikasa's world in the fanfiction.
In the fanfiction, Naruto may first assess the situation when he sees Mikasa in trouble. He realizes that the Titans are different from any enemy he has faced before. So, he decides to combine his Wind - Style jutsu with his physical strength. He creates a huge gust of wind that blows the Titans away from Mikasa. After that, they might start to explore each other's worlds. Naruto could be fascinated by the technology in Mikasa's world like the vertical maneuvering equipment, and Mikasa could be intrigued by Naruto's ninja skills and the concept of chakra.
Well, Naruto could use his Nine - Tails chakra to create a powerful shield around Mikasa when the Titans are attacking. This would protect her from their attacks. Then he could use his chakra arms to grab onto nearby buildings and swing them both to safety.
One possible storyline could be that Naruto, with his ability to teleport and his powerful ninjutsu, senses Mikasa in danger in the Attack on Titan world. He quickly arrives, uses his Rasengan to defeat the Titans surrounding her. Then he takes her to safety and they form an unlikely friendship, with Naruto sharing his experiences of fighting for his village and Mikasa being amazed at his powers.
One possibility is that Naruto uses his Shadow Clone Jutsu to create distractions while he rescues Pyrrha from a trap. Since he's so good at this jutsu, he can easily outwit the bad guys. Pyrrha, on the other hand, might be able to assist Naruto once she's free, using her weapon skills.
Perhaps Naruto saves Shisui from a group of rogue ninjas. He uses his speed and agility, enhanced by his training with Jiraiya, to quickly reach Shisui. His Nine - Tails chakra could also flare up, intimidating the enemies and giving him the power to fight them off.
One possibility is that Anko is poisoned during a mission. Naruto, having learned some medical ninjutsu from Tsunade, uses his skills to find an antidote and save her. He might have to search far and wide, facing various challenges along the way.
In the fanfiction, Sarutobi could be kidnapped by a group of ninjas from another village. Naruto would then embark on a solo mission to rescue him. He'd use his stealth skills and knowledge of the terrain to infiltrate the enemy's hideout and save Sarutobi without being detected.
Perhaps Naruto teams up with Shikamaru. Since Shikamaru was very close to Asuma, they could combine their skills. Naruto's brute strength and Shikamaru's intelligence would make a great duo. They could come up with a complex plan to save Asuma from whatever danger he is in, like a deadly curse or a powerful enemy's attack.
In a 'Goku Saves Naruto' fanfiction, Goku might teach Naruto some of his unique fighting techniques. Since Goku has such a vast knowledge of martial arts and energy control, he could help Naruto become even stronger. For example, he could show Naruto how to better control his chakra using the principles of ki control. And also, Goku's fearless attitude in battle could inspire Naruto to face his enemies more bravely. Goku could also use his Dragon Balls to wish for something that would benefit Naruto or his village, like restoring the damage done by a powerful enemy attack.
It could also result in a change in the way the village views their relationship. Since Naruto is a hero, his saving of Hinata would be a big deal. This could lead to the village elders or the people in general being more accepting of a possible romantic relationship between them. For example, they might start to see Hinata as a more important figure in Naruto's life and give her more respect.
Well, Naruto could save a woman who is trapped in a collapsing building during an enemy attack. He could use his super strength and speed to get her out safely. Then, the woman might be so grateful that she offers to help Naruto in his future missions in some way, like providing him with valuable information about the enemies.
In a 'naruto saves boruto fanfiction', Naruto might use his powerful jutsu like Rasengan to fend off enemies threatening Boruto. He could also use his experience and wisdom to guide Boruto out of a difficult situation, perhaps one involving a powerful new villain in the ninja world.