TLoZ: Spirit Tracks had you control Link primarily but you used Zelda’s ghost to possess things, help you fight, and solve puzzles. It would be hard for a solo dev, but you could have a knight with an AI that proceeded based on what paths you unlock for it. So the princess would be some sort of astral projection I guess. But then, you wouldn’t really feel trapped. Maybe you need to hide your activity from the dragon or distract it for a stealth aspect or resource management. You would need to balance swapping back and forth between your body and helping the knight. Might be easier to settle on an in-universe justification after figuring out the core gameplay.