Two Z chromosomes.

The shift in reality was rapid and quite marked. The phone he was holding seemed to grow bigger. “Huh?” John asked in surprise as the words on the screen suddenly seemed to change to some foreign language. “Uh Oh,” his voice was high and clearly feminine. His fingers were slim with long glossy pink painted nails. “Am I ZY? Or... oh no. A ZZ?” The phone dropped from his shocked hands as he looked at his clothes. He wore a sailor style school uniform, not unlike those that Japanese girls wore. But this one was tight and revealing. And the form that it revealed was that of a small, young and curvaceous girl.

Hands went to chest to find breasts. Very sensitive breasts with nipples that hardened reflexively with uninhibited arousal. “Oh... But... I wanted a submissive double Z. Not to be one!” She muttered to herself. She was tiny... and she’d inadvertently made herself property. A submissive, horny, hyper fertile and very sexy girl...

“Hey Jojo, be careful with my phone. It’s expensive to replace...” a man firmly scolds John... Jojo. She’s Jojo. And this is her owner.

Jojo swallows and picks up her masters phone, blushing furiously and checking to make certain it’s not broken. She sighs in relief when she sees it is not. “I’m sorry Master. I was surprised,” she explains feeling silly. She skipped up to him, breasts bouncing heavily, and give him back his phone... but wasn’t it John’s phone. No... master said it was his. Jojo looked up at her master.

He’s in his mid twenties. He’s handsome and muscular. Hmmm. He’d be a good fuck.