Well, one possible plot could be that the servant Naruto summons is from a future time. This servant has knowledge of events that are yet to happen in the Naruto world. Naruto then has to use this knowledge wisely while also keeping the servant's origin a secret from others who might misuse it.
Maybe the servant is actually a spirit of a long - dead ninja. Naruto summons this spirit - servant by mistake. The spirit has unfinished business in the world and Naruto has to help it while also using the spirit's skills in battles. The plot could involve Naruto learning about the past of the ninja world through this spirit - servant.
The plot could be that Raven is in a dire situation in her world. She discovers an ancient spell that might be able to bring a powerful ally to her side. She decides to use it to summon Naruto. Once Naruto arrives, they face a powerful enemy that is threatening Raven's world. They combine their powers, Naruto's Rasengan and Raven's dark magic, to defeat the enemy.
The plot could start with Shirou being in a desperate situation in his own world. He discovers an ancient spell or artifact that has the power to summon a powerful ally from another dimension, which turns out to be Naruto. Naruto then helps Shirou fight against the enemies that are threatening his world. Along the way, they face challenges that require both of their skills, like Naruto using his Rasengan against magical beasts and Shirou projecting shields to protect them from enemy attacks.
Well, in such a fanfic, Harry might summon a servant with unique powers. Maybe the servant could help him in his battles against Voldemort. For example, the servant could have the ability to detect dark magic from afar, allowing Harry to be more prepared for attacks.
It could be a house - elf. House - elves are known for their loyalty and their ability to do various tasks. They could be very useful to Harry, like helping him keep his dormitory clean or even spying on the Death Eaters.
One possible plot could be that Naruto loses a bet to Hinata in a friendly competition among the ninja trainees. As a result, he has to be her servant for a certain period. During this time, he has to do tasks like fetching her training equipment, preparing her meals, and assisting her in her studies. But through this experience, they both learn more about each other and their relationship deepens.
A possible plot could be that there is a disturbance in the balance of the Naruto world. The sages believe that only a being from another realm can help. Naruto is chosen to perform the summoning. He summons Mordred, and at first, they don't get along because of their different backgrounds. But as they learn more about each other and the true nature of the threat, they form an alliance. Mordred teaches Naruto some new combat techniques, and Naruto shows Mordred the value of friendship and loyalty in his world. Eventually, they defeat the enemy and Mordred may or may not decide to stay in the Naruto world depending on how their relationship has developed.
Well, in such a fanfiction, Naruto might learn unique skills from the summons. For example, he could learn stealth from a cat - like summon or brute strength tactics from a bear - like one.
The fanfiction might start with Ilya performing a summoning spell that she thought would bring something else, but instead, Naruto appears. Since Naruto is always eager to make friends and help others, he quickly bonds with Ilya. They could then embark on a journey to find a way to send Naruto back home. During this time, Naruto could teach Ilya about the importance of perseverance and believing in oneself, just like he learned in his own adventures in the Naruto world.
One possible plot could be that Mikoto somehow survived and she takes Naruto under her wing. She trains him secretly, using her Uchiha knowledge to make him stronger. This could lead to Naruto having a unique set of skills that no one else has.
Well, one possibility is that Naruto resigns due to feeling burnt out from all the battles and political unrest in the village. He might decide he's done his part and wants a simple life away from the chaos.