As I recall, the Starlights had the opposite deal from the Senshi. Their fighting forms were their real identities, where the other form was for a specific purpose. So regardless of what body they went to school in, they were alien women at heart.
Didn't even know there's a third one. And while I'm usually fine with futa, magically becoming one just doesn't make any sense in K-On... But yeah, the two here are great.
So it really is that she used an "ix-nay" version of "I love you" (with the "v" replaced with "f"), like I half-suspected? It seems too easy of a cipher.
Can someone clarify whether she's holding a suspicious object in her hands or if there was a problem with the shading on her skirt? If she's holding something, that totally warrants yandere.