as kat was walking you wonder what you can do, you try moving your arms and nothing happens, you try your legs and nothing, you try moving at all, you find that you can not move like a human but like a bra could, instead of arms you move your straps, you lift kat's breasts up.
"oh, i see you've learned to move?" she teases. In response you try moving your cups, "aah, aah." comes from kat, "d-do that again."
you flex once more, "oooohhhhh" moaned kat, "s-so good" you wonder if you could do anything more than move, you do everything you can think of, eventually trying to inflate her breasts, it works, Kat's breasts begin growing slowly, stretching you out but it doesn't hurt,
"w-w-what!? h-how are you doing that?" she asks in horror and wonder as you concentrate more and her breasts grow faster. As time progresses Kat begins to panic, she is out in the open and her jugs are getting bigger, starting to be too big for her blouse, you also wonder how you haven't torn yet, you must just be really stretchy or you're growing with Kat. "Dan! Stop it!" she whispers to you, "no" you think, she made you suffer you make her suffer. You put every bit of thought into making your sisters breasts larger, "Dan seriously, i'm out in public, people are staring and my blouse is going to pop, stop now!" You slow down for the sake of her dignity, she is still your sister, so instead you stop growing her, and try something else, you try moving yourself to massage her now titanic tits, judjing by how big you feel and how heavy she feels you estimate you made her an E cup from a B cup, you begin flexing yourself as much as possible, you can hear her fighting the urge to moan.....this might not be so bad after all....