Jango Fett is a character that would fit well in a Geonosis fanfic. Since he has a history with the planet and the events that took place there. You could also include some clone troopers, like Rex. They could be part of a rescue mission on Geonosis. And a Geonosian queen - in - waiting who has different ideas about the future of her people compared to the current regime.
Definitely include Obi - Wan Kenobi. He has a connection to Geonosis already from the movies. Anakin Skywalker would also be a great addition. And for a non - Jedi character, you could add a Geonosian rebel who is trying to overthrow the corrupt leaders on the planet.
I'm not entirely sure, but it could include some Jedi knights and Separatist leaders since Geonosis is a significant battleground.
A great plot for a Star Wars Geonosis fanfic could be exploring the underground world of Geonosis more in - depth. Maybe a group of smugglers discovers a hidden treasure or a powerful ancient artifact there. They then have to outwit the Geonosians and other villains who also want to get their hands on it. This could involve a lot of action - packed chases and battles in the unique Geonosian landscapes.
Ahsoka Tano would be an excellent addition. She has a rich history in the Star Wars universe, from the Clone Wars to her later appearances. Her wisdom and combat skills could be a great asset to the Rebels in a crossover. She could also provide a link between different eras of the Star Wars story.
Sabine Wren would be a great character to include. They have a connection in the Star Wars Rebels series, and their interactions could be further explored in fanfiction. Ezra Bridger is also a good choice. His journey and his relationship with Ashoka could be developed more. Another character could be Bo - Katan Kryze. Her Mandalorian ways and her goals could clash or align with Ashoka's, creating interesting storylines.
Definitely a Force - sensitive child who the Sith Stalker discovers. The Sith Stalker has to decide what to do with the child - train them in the ways of the Sith or let them go. Another interesting character could be an old Sith spirit that haunts the Sith Stalker, giving them cryptic advice. And a smuggler who ends up helping the Sith Stalker on one of their quests, for a price of course.
Definitely Darth Vader. His presence would create a lot of tension. He could be on a mission to hunt down the Rebels crew, and it would be a battle of wits and strength as they try to outmaneuver him.
Definitely Luke Skywalker. He could cross paths with Iden and they could have some interesting ideological battles. Leia Organa would also be a great addition. Her strong leadership and rebel spirit could contrast with Iden's Imperial upbringing. And of course, Han Solo. His roguish charm could make for some entertaining interactions with Iden.
In a Dooku - centered fanfic in The Clone Wars, Qui - Gon Jinn could be an interesting addition. Even though he's dead, Dooku could be haunted by memories of his former apprentice. This could add an emotional layer to the story. Count Dooku's own family members, if any are explored in the Star Wars lore, could also be included. Their influence on his decisions, or how he thinks about them while being a Sith, could be fascinating. Also, other Sith Lords or acolytes that Dooku might interact with in the shadows during the Clone Wars would be cool to include.
In addition to the obvious ones like Luke, Leia, and Anakin, you should consider including Padmé Amidala. She was Anakin's wife and played a big role in his life before his turn. Yoda also has an important connection to the Skywalker family as he was one of Anakin's teachers and later trained Luke. Ben Solo (Kylo Ren) is also a key character. His internal struggle between the Light and Dark Side is a continuation of the Skywalker family's complex relationship with the Force.
Ahsoka Tano would be a great character to include. She's strong - willed and has a unique connection to the Force. Her presence on Mortis could bring new perspectives and her skills as a fighter would be useful in the challenges there.