Well..I suppose the best way to describe could be like constantly tensing a muscle. As you know I can’t revert to that form by myself. Bisky explains.

When I relax I go back to being tall and muscular. If I was to be knocked completely unconscious, I would change back. Otherwise I can hold my petite form even in my sleep. She scratches her cheek lightly. Of course I need help from cookie to keep my stamina up.

When this ability to change back and forth started to manifest, I was excited! She winced as her tone rose in excitement a moment. Her new sensitive ears rang with pain, forcing her to lower her volume.

But to be completely honest, I’m not certain how it manifested. All that..body mass is still there. It doesn’t just go away. I’ve always assumed it had to due with my nen being that of a transmuter.