A Sith assassin could be a compelling OC. This character is highly skilled in combat and stealth, trained in the ways of the dark side. They could work with Anakin on secret missions for the Sith. Their cold - blooded and efficient nature might rub off on Anakin, making him more ruthless in his actions.
A powerful Nightsister could be a great OC. The Nightsisters have their own connection to the dark side of the Force. An OC Nightsister could use her magic and knowledge of the dark side to interact with Anakin. She might offer him new ways to use the Force, like some of the unique spells and abilities that Nightsisters possess.
One possible plotline could be the OC's influence on Anakin's fall to the dark side. Maybe the OC has a unique view on the Force that starts to sway Anakin's beliefs. For example, they could introduce him to a more extreme interpretation of the power that the dark side offers.
One common theme is redemption. Since Anakin's story in the official Star Wars lore is about his fall and redemption, many fanfictions with OCs explore this further. The OC might be the catalyst for Anakin's redemption or be involved in his journey in some way.
Sure. 'The Force of an Unlikely Bond' is a great one. It shows how Anakin interacts with an original character in a really interesting way. The OC has a unique backstory that ties into the Star Wars universe and their relationship with Anakin develops over time, filled with action and emotional moments.
The OC master could be a hermit who has been living in isolation for years, developing a unique understanding of the Force. He or she might have witnessed the downfall of the Jedi Order in the past and wants to prevent Anakin from making the same mistakes.
The SI could also be a love interest for Anakin. In a fanfiction, this could be a very different kind of relationship compared to what he had with Padmé. This relationship could either be a positive influence, giving Anakin more stability and a reason to stay on the light side, or it could be a source of conflict, especially if the SI has their own secrets or agendas.
Perhaps it's a non - Force - sensitive character who has skills in other areas that are important in the Star Wars universe. For example, a great pilot or a brilliant strategist. This person could be getting more attention or praise than Anakin in certain situations, and thus be seen as a rival.
As he spends more time as a Sith, he might start to feel a sense of emptiness. He realizes that the power he sought isn't fulfilling. He could then have a moment of self - reflection. Maybe he meets a character who challenges his beliefs, like a young Force - sensitive who still believes in the good in the galaxy. This makes him question his path and start to seek a way back from the dark side.
One plot idea could be that your SI OC is a young Force - sensitive being discovered by the Jedi Order, but they have a connection to an ancient Sith prophecy. The Jedi must decide whether to train them or fear their potential for darkness. Another idea is that your OC is a bounty hunter who gets caught in the middle of a power struggle between the Hutts and a new criminal syndicate. They have to use their wits and skills to survive and maybe even tip the balance of power.
One idea could be Anakin as a Sith having to face his former Jedi allies. He might struggle with his new identity while still having remnants of his Jedi self. For example, he could be sent on a mission by the Sith to destroy a Jedi stronghold but find himself hesitating when he sees his old friends there.
The SI could be a smuggler who crosses paths with Anakin during one of his missions. They team up and the SI shows Anakin a different side of the galaxy, one that's not all about the Jedi and Sith. This could make Anakin question his place in the galaxy and his loyalty to the Jedi Order. Their adventures together could range from dealing with pirates to uncovering ancient secrets.