It could be some new and unknown enemy. Maybe a group of bandits with special abilities that allow them to overpower Naruto for a short time and tie him up. Also, in some fanfictions, a jealous rival within Konoha, someone who is envious of Naruto's popularity and power, might tie him up in an attempt to make him look weak or to get him out of the way so they can shine.
Enemies from other villages could tie Naruto up. For instance, the Sand Village might have some rogue ninjas who see Naruto as a threat to their plans. They could capture and tie him up to stop him from interfering. Another possibility is that Orochimaru or his followers could tie Naruto up. Orochimaru has always been interested in Naruto's power and might try to capture and restrain him to conduct some sort of experiment on him.
He could pair up Shikamaru and Temari. They already have a bit of a connection and Naruto, seeing their potential, could nudge them further into a relationship. He might arrange for them to have more diplomatic meetings that turn into personal get - togethers.
Sasuke could be one. Given their complex relationship, there could be a situation where Sasuke's newfound power or different ideology leads him to fight and beat Naruto in a fan - made story.
A former friend or teammate who has turned to the dark side could be an antagonist. For example, if someone like Sasuke had completely given in to the dark side and decided to attack Naruto for some reason. Or it could be a new and mysterious character who has a vendetta against the Uzumaki clan and sees Naruto as the prime target to take revenge on the clan. This character could be very powerful and use their abilities to beat Naruto up.
Naruto might end up teaming with some of the more sane inmates who have a sense of right and wrong. For example, he could form an alliance with a reformed criminal who wants to help Naruto navigate the complex and dangerous world of Arkham. Together, they could try to expose the corrupt elements within the asylum.
Perhaps some of the more conservative and anti - Uzumaki elders in the village. They might still hold grudges against the Uzumaki clan and see Naruto as a potential threat. So they tie him to the log as a way to show their power and authority over him.
Naruto might team up with Gaara. Gaara has his own unique abilities with sand control. Together, they could form a strong duo for a secret mission, especially if it involves something related to the balance of power between their respective villages.
A disgruntled ex - friend could be the kidnapper. Maybe there was a falling - out between the two characters, and the ex - friend wants to get back at the owner of the hair tie. They think that by taking this precious item, they can cause emotional pain.
A story about a wife and husband cooking a special meal together. They collaborate in the kitchen, sharing laughter and creating a delicious dish, which shows their harmony and cooperation.
In a mystery or thriller story, she might be a spy or an agent who needs to capture the man because he has some crucial information. Tying him up would be a way to keep him in one place until she could extract the information she needed. She might also be trying to prevent him from warning his accomplices.
In a Naruto x Shake It Up fanfiction, Naruto and Flynn could also be main characters. Flynn is always full of surprises and his comical nature along with Naruto's heroic and sometimes clueless nature about the modern world (since Shake It Up is a more modern - day setting) would create a lot of humorous and adventurous situations. Also, Gaara from Naruto could be brought in. His brooding personality would contrast well with the energetic Shake It Up characters.