"-Want to try out having gigantic breasts for the day!" Dawn finished saying. Luca just stared at her for a bit as Dawn blushed a bit and said "I'm don't have plans or anything, Mom and Dad will be gone the next few days for that bible thing we're not interested in, and... I just want to know what it feels like."
"I'll still be around the house..." Luca felt he should add
"So? We're close." Dawn said leaving as much or as little as Luca wanted to read into that statement as he wanted to.
Luca got onto the chronivac then asked "So... by gigantic did you mean like G-"
"Like what's the biggest that thing can make?"
"Umm... there doesn't seem to be an upper limit... I'd be tempted to put in universe sized, but..."
"But then we'd all be crushed by my universal rack..."
"How about we start you at ZZZ and then grow you overtime if you really want?" Dawn nodded so Luca edited Dawn's breast size for a third time, and then heard Dawn moaning a bit behind him.
A breathy "You may as well watch" came out of Dawn and Luca turned around and saw his step-sister grow. Her not insubstantial chest was surging forward. The silly little training bra thing she had on was down on the ground completely useless as her shirt was now her bra... Then it gave away as Dawn's now relatively massive nipples dragged underneath the shirt in a case of extreme underboob. Her breasts reached nearly to her navel as she held her extremely ample bosoms with her arms as her face was flush... a bit with embarrassment... a bit with hornyness... She smiled a bit, it was a little wavering wondering what Luca thought but Dawn said "So... I got my initial change... did you want to do anything big boy?"