You lean in close and your lips meet the princess's; warmth seems to flow through you and then you suddenly stumble back. You feel strange, dizzy, and the princess looks at you with concern. Then you start to change.
The first thing that happens is that you can feel yourself growing to a height of about six feet, though you don't gain much bulk, leaving you tall and rangy. Then your waist contracts while your hips expand; not overly so, but enough to give you a noticeable feminine figure. Your mind spins - are you turning into a woman? - and then your question is seemingly answered as a pair of breasts force their way from your chest, small but firm. The hair fades from your arms and legs, leaving them smooth, but muscle fills in as they become shapely but strong. You're not just becoming a woman, clearly, but an athlete - no, a warrior. A feeling of power courses through your body as your genitals invert between your legs.
Your face tingles sharply and reshapes, becoming feminine but stern, more handsome than beautiful, while your hair turns jet black and styles itself into a bob. Then your clothing starts to change, first becoming padded undergarments and then vanishing as steel plate armor materializes around it. A red cape appears and flows from your shoulders to your ankles, and a sword appears and hangs from your belt. Your transformation is complete; you have become a warrior woman, a lady knight in shining armor who can challenge any opponent.
The princess stares at you, eyes wide. "You are not my prince charming," she says, "but I think I know you. You... you are Lady Cassia, my old friend and protector! How can this be?"