One great fanfic could be about their adventures before Naruto was born. It might explore their relationship dynamics, how they trained together and supported each other. Maybe in this fanfic, Jiraiya tries to convince Tsunade to take on more dangerous missions with him, showing his trust in her abilities.
In fanfiction, Jiraiya's death can also be used to explore themes of sacrifice. He sacrificed himself for the greater good, and this can be further elaborated in different stories. For example, some fanfictions might show how his death inspired other characters to be more selfless.
Naruto is devastated. He feels a huge void in his heart. Jiraiya was the one who believed in him from the start, and his death makes Naruto question a lot of things. He might even start to doubt his own strength for a while.
Jiraiya's story concludes in Shippuden. It's a heartbreaking part of the storyline that leaves a lasting impression. His death sets the stage for many important events and motivations for the other characters.
One popular theme is their unrequited love. Jiraiya's long - standing feelings for Tsunade that she doesn't fully reciprocate until later in some stories. It adds a lot of emotional depth and drama to the fanfics.
One scenario could be that Jiraiya is poisoned before his fight with Pain. In the fanfiction, an enemy within the village who is secretly working for Pain's forces might have poisoned his food or drink. So, when he goes to face Pain, he is already weakened, and this ultimately leads to his death. Another possibility is that Jiraiya's death is a result of a time - traveling plot. If there is time - travel involved in the fanfiction, his actions in the past might accidentally create a situation where he has to die to preserve the timeline.