I think that's a powerful arc, personally. Example: the Sith apprentice is an orphan of some kind. Maybe they don't know their parents, or maybe they feel disconnected from their parents for some reason. Or maybe what makes them an orphan is that they were an apprentice of Palpatine, who died (we've heard rumors of a Sith apprentice). What if this orphan thought themselves evil through and through, but after developing a relationship with the Sky-Solos, begins to have new feelings? They still stick to their plan though, which is to destroy the Sky-Solos/Jedi. So they kill someone new or old who is well-respected, and the guilt is overwhelming. This murder or attack may be what opens them to the lightside for the first time. But now there's a new problem: the Jedi are hunting them, and their Sith master (spirit or not) senses the change in their heart. Both sides descend on our orphan. What now?