Another possibility is rogue Jedi who have turned to the dark side. They could be former comrades of Mace Windu, and he has to face them in combat. This would add an emotional layer to the story as he has to fight people he once considered friends and allies.
Well, it could focus on Mace Windu's early days in the Jedi Order. Maybe show how he was trained, his first encounters with the dark side threats, and his rise within the Order.
Palpatine could still be the main antagonist. Even if Mace Windu travels through time, Palpatine's long - term plans for galactic domination would still be a major threat. Windu would have to find new ways to outwit him in different time periods.
Mace Windu was a powerful Jedi Master. He was known for his purple lightsaber and his skills in combat. He was a member of the Jedi Council. He played a significant role in the Clone Wars, leading the Jedi in many battles against the Separatist forces. He was also involved in the discovery of the Sith Lord Palpatine's true identity, which ultimately led to his confrontation with Palpatine in the Chancellor's office.
In such fanfiction, it could lead to a completely different power dynamic in the galaxy. Maybe the Jedi would regain their prominence and prevent the rise of the Empire.
He could be a Force - ghost. His spectral form could guide Kanan or Ezra at crucial moments. For example, when they face a difficult decision regarding the Dark Side, Mace Windu's Force - ghost could appear and offer his wisdom based on his own experiences with the Sith.
One of the most memorable moments was when he faced Palpatine. His purple lightsaber clashing with Palpatine's in that intense duel was epic. Another moment was his leadership during battles in the Clone Wars, where he showed great strategic acumen.
If Mace Windu didn't die, he might have trained more Jedi and prevented some of the Order's downfalls. His presence could have altered many events in the galaxy.
One similarity could be the loyalty aspect. Mace Windu is loyal to the Jedi Order and its principles. In Pulp Fiction, Vincent Vega is loyal to his boss Marsellus Wallace to a certain extent. Also, the action scenes in both are quite iconic. Mace Windu has some amazing lightsaber battles in Star Wars. In Pulp Fiction, the fight scenes, like the one in the pawnshop, are very memorable. But overall, they are from very different cinematic universes, so the differences far outweigh the similarities.
Maybe Darth Vader. If the story is set at a time when Vader is at the height of his power, he could be the main obstacle in Mace Windu's path of revenge. Vader's loyalty to the Emperor and his own dark side powers would make him a formidable foe for Windu.
He could potentially team up with other Jedi survivors and go on a mission to find and protect Force - sensitive children from the clutches of the Empire. This would be his way of rebuilding the Jedi Order in secret.