In the fanfiction, Tsunade might rescue baby Naruto from a dangerous experiment that was being carried out on him. As she rescues him, she realizes that Naruto has an extraordinary ability to resist the negative effects of the experiment. This leads her to believe that Naruto is destined for something great and she devotes herself to protecting him at all costs.
One possible plot twist could be that the baby has some unique power that neither Naruto nor Tsunade possess. Maybe it has the ability to control time, which causes all sorts of chaos and also attracts the wrong kind of attention from villains who want to use the baby's power for their own evil deeds.
One possible plot twist could be that since they are the same age, Naruto might become Tsunade's rival in the medical ninjutsu field. Naruto, with his determination, could develop his own unique style of healing that challenges Tsunade's traditional methods. This could lead to a friendly competition between them, which in turn would force both to improve their skills and knowledge.
Perhaps a plot twist would be that there is some sort of curse associated with Naruto's lineage as their grandson. This curse could be related to the same forces that Tsunade and Jiraiya fought against in their lives. Naruto has to struggle not only with his normal ninja duties but also with this hidden curse. It could manifest in strange ways, like affecting his chakra control or making him a target for certain enemies. On the other hand, it could also be a source of great strength if he can overcome it. And there could be a prophecy related to him being the grandson of Tsunade and Jiraiya that he has to fulfill, which adds another layer of complexity to the story.
Perhaps a plot twist could involve Naruto's parents. If Naruto is Tsunade's little brother, then it might change the story of how his parents met and what their relationship was to Tsunade. Maybe his father was involved in some sort of mission with Tsunade and that's how Naruto came to be. It would also add a whole new layer to Naruto's relationship with Jiraiya, as Jiraiya was also connected to both Naruto's father and Tsunade in different ways.
A plot twist could be that Naruto discovers a secret about Tsunade that she has been hiding all along. It could be something related to her family or a power she has been suppressing. This discovery could either strengthen their relationship or create a rift between them. Also, there could be a twist where an outside force tries to use their relationship to gain power in the ninja world. They might try to manipulate Naruto or Tsunade to their advantage.
One possible plot twist could be that the kidnapper is actually related to Naruto in some way. Maybe a long - lost relative who has some sort of vendetta against the Hidden Leaf Village and thinks taking Naruto will give them leverage. Another could be that the kidnapper is being controlled by a greater evil force that wants to use Naruto's special powers for their own dark purposes. For example, they might want to extract the Nine - Tailed Fox's chakra from Naruto while he's still a baby and vulnerable.
One possible plot twist could be that Naruto develops a different fighting style. Since Tsunade is strong in physical combat and medical ninjutsu, and Jiraiya is a master of various ninjutsu and toad summons, Naruto might combine their teachings in unique ways. For example, he could use medical ninjutsu to enhance his own physical abilities during combat, similar to how Tsunade uses her strength. Another plot twist could be in his relationships. With Tsunade and Jiraiya as his guardians, he might have a different attitude towards the Hidden Leaf Village's elders. He could be more critical or more understanding depending on how they've influenced him. Also, his training might be more focused on stealth and intelligence gathering, skills that Jiraiya was good at, rather than just brute strength.
A plot twist could be that they are both chosen for a secret mission that only people of their age can undertake. They have to work together to infiltrate an enemy stronghold. Along the way, they discover a long - lost family connection between them. This revelation changes their relationship and makes them even more determined to succeed in the mission for the sake of their family and the village.
One possible plot could be that Tsunade discovers baby Naruto alone and decides to take him under her wing. She could train him from a very young age, teaching him not only ninja skills but also important life lessons. Maybe she'd protect him from those who still hold grudges against the Nine - Tails within him. This would lead to a Naruto with a different kind of upbringing and a very strong bond with Tsunade.
One possible plot twist could be that Tsunade trains Naruto not just in physical combat like she did with others, but also in medical ninjutsu. This would be unexpected as Naruto is more known for his brute force. Maybe Naruto uses his new medical skills in a creative way during a battle, like healing his opponents to show mercy and then defeating them when they are off - guard.