In some versions, it could be a former ally who has been corrupted. This character, once on Ahsoka's side, has now turned against her due to some external influence or personal greed. Their knowledge of Ahsoka's strengths and weaknesses would make them a formidable opponent, and they could be the one to cause her death.
Their relationship could start from a place of enmity. Ahsoka, as a Jedi - adjacent figure, would be opposed to Thrawn's imperial ways. But as they face common foes or challenges, they might develop a grudging respect. For example, when they are both trying to solve a mystery that has the potential to destroy a whole star system.
Perhaps in the fanfiction, Ahsoka and Thrawn end up on a desolate planet. They have to rely on each other's knowledge - Ahsoka's Jedi wisdom and Thrawn's strategic military mind - to survive and find a way off the planet. As they do so, they begin to understand the motives behind their respective actions in the greater galactic conflict.
In a 'ahsoka death fanfic', one possible scenario could be her sacrificing herself in a battle against a powerful enemy. Maybe she faces an overwhelming force that she decides to take on alone to protect others.
Perhaps in a more complex scenario, Ahsoka could be trapped in a time - loop that is slowly draining her life force. She tries to break free but realizes that the only way to stop the loop from spreading and destroying everything is to give up her own life. This would be a very tragic and thought - provoking way to write her death in a fanfiction.
Self - sacrifice is also often seen. Ahsoka might choose to die to save a planet or a group of people. This would be in line with the heroic nature of her character in the Star Wars universe.
Eli Vanto is important. He is sort of an assistant to Thrawn and learns a great deal from him. Admiral Ar'alani also plays a role as she is from Thrawn's own people, the Chiss. And there are various Imperial officers who interact with Thrawn and either support or oppose him.
Well, in certain fanfictions, Ahsoka could die due to betrayal. Maybe someone she trusted turns on her, and in the ensuing fight, she is mortally wounded. It would be a very emotional moment, especially for those characters who are close to her like Anakin. This kind of death would add a lot of drama and angst to the story.
In some fanfictions, Ahsoka's death might be a tragic sacrifice. Maybe she faces an overwhelming enemy force alone to save her friends. For example, she could be caught in a Sith - led ambush while on a crucial mission. However, in the official Star Wars lore as of now, Ahsoka doesn't die during The Clone Wars.