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.
Perhaps in this fanfiction, Tsunade stumbles upon baby Naruto during a mission. She is immediately drawn to his spunk, even as a baby. She then takes him back to the village and begins to raise him in secret, away from the prying eyes of those who might want to harm him. As Naruto grows, he starts to show amazing ninja potential, and Tsunade has to decide how to introduce him to the village while still keeping him safe.
A plot might involve Naruto finding an old Christmas tradition that was lost in the village. He goes to Tsunade to ask her about it, and she remembers bits and pieces. Together, they search for more information. Along the way, they meet various villagers who share their own memories related to the tradition. In the end, they manage to revive the tradition, and it becomes a new and exciting part of the village's Christmas celebration.
Perhaps in this fanfiction, Tsunade discovers she's pregnant unexpectedly. She then has to deal with the shock and also the excitement. She might worry about how she can balance her duties as a leader with being a mother. The story could focus on her preparing for the baby's arrival, from setting up a nursery to learning about parenting, all while still having to deal with the threats to her village.
One possible reason could be a misunderstanding. Maybe Tsunade received some false information about Naruto that made her think he was a threat to the village, so she took actions that ended up hurting him.
One possible plot could be Naruto using his charm and determination. Maybe he starts by impressing Tsunade with his growth as a ninja. He could show her his new jutsus and how far he's come in his training. Then, he gradually starts to show his affection in a more personal way, like bringing her small gifts or helping her with her Hokage duties in a very dedicated manner.
In this fanfiction, it could be that Naruto's death as a baby is the result of a conspiracy. Maybe some anti - Uzumaki or anti - Jinchuriki group within Konoha planned his death. This would then lead to a series of events where the truth is slowly uncovered by some of the more perceptive characters in the village. This could create a lot of internal conflict as characters have to choose between loyalty to the village and uncovering the truth about Naruto's death.
Well, it could be about Naruto accidentally breaking something precious of Tsunade's, like a family heirloom. This might lead to a series of events where Tsunade is initially angry but then Naruto makes it up to her in some heroic way, perhaps by going on a difficult mission for her.
In this type of fanfiction, perhaps Naruto is exiled due to some false accusations. Maybe there's a misunderstanding about his power or some events he's involved in are misconstrued. Tsunade, as the Hokage, might feel pressured by the village elders or some political situation to exile Naruto.
Well, it could be about Naruto having to deal with the unique situation of being Tsunade's son. Maybe he'd inherit some of her strong - willed nature. He might also face different expectations from the village.
Maybe a dark force takes over Naruto's mind. This force could be an ancient evil that has been sealed away for centuries and now wants to create chaos in the ninja world. It uses Naruto as a puppet to kill Tsunade, one of the most powerful protectors of the village. The story could then focus on Naruto's friends trying to free him from this control and avenge Tsunade.
Perhaps in the fanfiction, it's a plot device to show a different side of Tsunade. She might be under the influence of a strange jutsu that makes her act out of character and kiss Naruto. This could then lead to a comical chain of events as Naruto tries to figure out what's wrong with Tsunade and the other characters react to this unexpected display of affection. The fanfiction could then focus on how Naruto has to deal with this new situation and keep it a secret from some of the more conservative characters in the village.