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 this fanfiction scenario, Ahsoka meeting Krell's men could lead to a lot of interesting plot developments. Maybe she tries to understand their motives under Krell's command. She might even attempt to turn them against Krell if she discovers his true nature. It could be a story full of action, with Ahsoka using her combat skills to gain their respect and then persuade them to do the right thing.
They might start off warily. Galen, being used to the ways of the Sith, would be cautious around Ahsoka, a Jedi. Ahsoka, on the other hand, would be on guard but also curious about Galen. Eventually, they could start to exchange combat techniques and stories of their past experiences.
Obviously, Luke Skywalker and Ahsoka Tano are the main characters. Luke is a key figure in the fight against the Empire and in the revival of the Jedi Order. Ahsoka, on the other hand, has a long and complex history within the Star Wars universe, having been Anakin Skywalker's apprentice and later becoming a key figure in her own right.
It could be a new Sith Lord. This Sith Lord has been secretly amassing power in the shadows and now aims to destroy the last remnants of the Jedi. His dark powers pose a great threat to Rey and Ahsoka, and they must use all their skills and the Force to defeat him.
Perhaps it's a story where Rey and Ahsoka team up to fight a new threat. The galaxy is in danger once again, and their combined skills and different perspectives on the Force make them a formidable duo. They journey across different planets, encountering various obstacles along the way, and in the process, Rey learns a great deal from Ahsoka about combat and strategy.
Well, it could be that Anakin and Ahsoka meet in a dangerous situation in the fanfiction. They would then have to work together to get out of it. For example, they might be trapped on an unknown planet filled with hostile creatures. They'd use their combined skills, Anakin's raw power and Ahsoka's agility, to fight their way through and find a way back home. This kind of scenario would not only show their relationship but also their growth as characters since they last parted ways.
Their interaction would likely be a bit cautious at first. Ahsoka has her own experiences with the Jedi Order and the Clone Wars, and Luke has his own journey in the new Jedi Order. But soon, they would recognize the common ground in their love for the Force and their desire to do good. They might start by sharing their respective stories, like Luke talking about his battles against the Empire and Ahsoka about her time with Anakin.