Maybe there's a situation where Jiraiya writes a novel that Tsunade reads. In the novel, he describes a love story with a kiss that is clearly inspired by his feelings for her. Tsunade, touched by this, confronts him and then they share a kiss. This could lead to a series of events where they have to deal with their new - found feelings in the context of the ninja world, with all its politics and rivalries.
A fanfiction about their marriage could explore their past traumas and how they heal together. Jiraiya has his own demons from his past missions and relationships, and Tsunade has lost loved ones. Through their marriage, they could find solace in each other. For example, Jiraiya could comfort Tsunade during her nightmares about losing her brother and lover, and Tsunade could give Jiraiya the stability he always craved. Their relationship would be a journey of growth and mutual understanding.
A plot could involve Tsunade and Jiraiya in their younger days. Maybe they both had a crush on each other but were too shy or focused on their ninja training to admit it. As they grow older and more experienced, their feelings resurface. Tsunade might start to notice how Jiraiya has always been there for her, through her losses and tough times, and this realization blossoms into love.
Perhaps in a fanfiction, it could be a part of a bet. Tsunade, always the confident one, makes a bet with Sakura. If Sakura can master a really difficult medical jutsu within a short time, Tsunade will give her a special reward. Sakura manages to do it, and Tsunade, impressed and proud, gives her a congratulatory kiss. This would add an interesting dynamic to their relationship in the story.
One possible plot could be that after years of adventures and unspoken feelings, Jiraiya finally decides to settle down. He proposes to Tsunade in a very Jiraiya - style, perhaps writing a novel about their story and presenting it to her. Tsunade, who has always had deep feelings for Jiraiya despite their bickering, accepts. Their married life could be filled with Jiraiya still going on occasional missions while Tsunade manages the village, and they have to navigate the challenges of being in a relationship while having important responsibilities.
One possible plot could be that Tsunade and Jiraiya are deceived by false information about Naruto. Maybe they are made to believe that Naruto has turned to a dark side. For example, an enemy might have created false evidence of Naruto collaborating with a powerful evil force. Tsunade, being the Hokage, and Jiraiya, Naruto's mentor, would then be forced to take actions against Naruto that seem like betrayal from Naruto's perspective.
A possible plot could be that Naruto, under the care of Tsunade and Jiraiya, discovers new aspects of his heritage. Tsunade might know some secrets about the Uzumaki clan that she shares with Naruto. Jiraiya, being his godfather - like figure, helps him explore these new revelations. Meanwhile, the Akatsuki could still be a threat, and Naruto, with his new skills and knowledge, has to fight against them to protect the village and his loved ones.
One possible plot could be that Jiraiya and Tsunade decide to adopt Naruto after seeing his loneliness and potential. They start training him not just in ninja skills but also in life values. Jiraiya might teach him more about the toad sage techniques, while Tsunade could help him with his chakra control and medical ninjutsu knowledge. Naruto would grow up in a more stable family - like environment, which would change his personality a bit, making him more confident and less brash as he has the support and love of two powerful ninjas.
One possible fanfiction could be set in their early days. Jiraiya, with his brash and confident self, tries to court Tsunade in his own clumsy way. Tsunade, initially resistant, starts to see his true heart beneath the bravado. They could go on adventures together, and during a dangerous moment, Jiraiya's protection of Tsunade makes her realize her deeper feelings for him.
One interesting storyline could be a mission where Naruto, Jiraiya and Tsunade are forced to work together. Naruto learns a lot from Jiraiya's combat techniques and Tsunade's medical knowledge. Another could be a story set in the past, showing how Jiraiya and Tsunade interacted when they were younger, and how Naruto's presence in the present changes their relationship dynamic. A third could be a story where they face a powerful enemy together, and Naruto has to use his newfound skills under the guidance of Jiraiya and Tsunade to defeat the foe.
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.