In 'ahsoka and anakin kiss fanfiction', a prevalent theme is the struggle between duty and desire. They are both Jedi with important responsibilities, and a kiss between them represents a moment where their personal desires for each other conflict with their duties. Another theme is the power of love to change destinies. The kiss might be seen as a turning point that alters their fates, either for better or for worse. There's also the theme of secrecy, as they would have to keep their relationship hidden from the Jedi Council.
One common theme is the exploration of forbidden love. Since they have a master - apprentice relationship in the canon, a romantic relationship is against the Jedi Code. Another theme could be the idea of sacrifice, where the kiss might be a moment of realization before one of them has to make a difficult choice.