Maybe in the fanfiction, Jiraiya is summoned by a new jutsu gone wrong. When he meets Boruto, he mistakes him for Naruto at first. As they interact, Jiraiya realizes Boruto's own unique struggles. He shares his wisdom about handling the expectations that come with being a ninja from a famous family, and Boruto learns a great deal from him.
In this fanfiction, Boruto might learn some unique ninja techniques from Jiraiya. Jiraiya could see the potential in Boruto and train him in his own unorthodox ways. Maybe Boruto would be introduced to Jiraiya's toad summoning, which could add a whole new dimension to his combat abilities.
Perhaps an old enemy of Jiraiya who was thought to be defeated but has now resurfaced. This antagonist targets Boruto to get to Jiraiya, thinking that by harming Boruto, he can draw Jiraiya out and finally get his revenge. He would be a powerful and cunning foe, making it difficult for Jiraiya and Boruto to face him.
Jiraiya could act as a mentor to Boruto. He might correct Boruto's mistakes in combat or give him advice on how to handle difficult situations. Boruto would listen intently, trying to soak up all the knowledge from this legendary ninja. And they could also have some light - hearted moments, like joking about Naruto's clumsy moments when he was young.
One possible scenario in this fanfiction could be Jiraiya taking on the role of a mentor to young Naruto even more intensively. He might teach Naruto some unique jutsu that are not part of the original storyline. For example, he could introduce Naruto to some ancient toad - related techniques that are only known within the toad clan.
In this fanfiction, perhaps Jiraiya didn't actually die. He was in a hidden place recovering from a serious injury. When he meets Naruto again, Naruto is shocked but overjoyed. Jiraiya then shares his newfound knowledge and powers with Naruto, and they team up to take on a powerful organization that threatens the Hidden Leaf Village. Jiraiya could teach Naruto some advanced Sage Mode techniques that he had been working on during his absence.
Obviously, Naruto and Jiraiya are the main characters. Naruto is the young and energetic ninja with big dreams, while Jiraiya is the experienced and somewhat pervy sage who has a lot to teach Naruto.
The plot might involve Naruto and Jiraiya getting transported to a different dimension. In this strange new world, they have to work together to find a way back home. They meet all kinds of strange creatures and characters. Jiraiya uses his wisdom and experience to navigate through this new environment, while Naruto's determination and growing power help them face the challenges. And during this adventure, Naruto might also develop a new form of his Rasengan, inspired by the things they encounter in this dimension.
Perhaps in this fanfiction, Neji is brought back to life somehow. Boruto, being curious, approaches Neji. Neji then discovers how much the ninja world has changed since his time. Boruto could show Neji the new technology in the Hidden Leaf Village. Neji might be a bit shocked at first but then start to see the potential in these new things. They could also form an unlikely friendship, with Neji guiding Boruto in matters of honor and discipline, which are values Neji held dear.