One idea could be that Hermione travels back in time and accidentally changes something that affects James's future. Maybe she saves someone important to James that was supposed to die, and then they have to deal with the altered timeline together.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a vast collection of fanfics, and you can simply search for 'Hermione and James time travel' in the search bar. Another option is Fanfiction.net, which also has a lot of Harry Potter - related fanfiction.
Fanfiction about James Sirius time travel can also play with the concept of destiny. Does time have a set path that cannot be changed, even with time travel? Or can James Sirius rewrite his family's future? These philosophical questions add depth to the stories and keep readers engaged as they ponder along with the character.
In time travel fanfiction, Hermione facing a boggart could be really interesting. Maybe the boggart takes the form of her failing in her time - travel - related tasks. For example, she might be afraid of causing a paradox that destroys the wizarding world she loves.
One great Hermione Snape time travel fanfiction is 'A Twist in Time'. It beautifully weaves a story where Hermione travels back in time and has to navigate her relationship with Snape. The author does an amazing job of exploring their complex personalities and how they interact in a different time period.
One great fanfiction could be where Hermione travels back in time and tries to understand Severus better. She might see his early years at Hogwarts and how he was bullied. This could lead to her having a newfound respect for him and trying to change his fate in some way.
One great fanfiction could be where Hermione travels back in time to save Sirius. Maybe she uses her time - turner in a new and creative way. In this kind of fanfiction, she might have to outwit the Ministry of Magic and the Death Eaters who are after Sirius. She could change the course of the story by preventing Sirius from going to Azkaban in the first place.
One great fanfiction could be 'Time's Twist'. In this story, Hermione travels back in time and meets the Marauders. The author does an amazing job of showing how Hermione's modern knowledge clashes with the Marauders' era. It has some really interesting plot twists like how Hermione tries to prevent certain events from happening but ends up causing new ones. Another one is 'Marauder Era with a Time - Traveling Hermione' which focuses more on the relationships she forms with the Marauders. She becomes friends with them and they learn a great deal from her. There's also 'Hermione's Time - Jump to the Marauders' Time' which is known for its detailed descriptions of the Marauder's time period through Hermione's eyes.
In many of these fanfictions, the Time Turner is often the key device for time travel. It allows them to go back in time for a set number of hours. However, some fanfictions introduce new magical artifacts or spells that can bend time in different ways, like a special potion or an ancient wand.
A great fanfiction idea could be that James Potter time - travels during a crucial battle in the wizarding world. He travels back to a time when the dark forces were just starting to rise. With his future knowledge, he could start preparing the wizarding community earlier. He could train young wizards and witches in advanced defensive magic, and try to change the course of history so that the big battle he left behind would have a different, more positive outcome.