So in one of the earlier seasons of Star Wars: The Clone Wars, Ahsoka Tano and her fellow Padawan, Barris Offee, team up for a few episodes. In these episodes, their friendship buds, they get buried alive together and attacked by infectious worms that can possess people, and are finally made to fight one another. And after all this, the two of them end up in this position:
And thus, the slash was born.