Next day

It was a long day for John. He wanted to use the app on many occasions but he limited it to only for few minor changes. He made his math test much easier. Why would he fail a school when he has the solution for everything? He also made his math teacher wear an unprofessional dress and be more openly forwards to her students if you know what I mean. Carl, his bully, was giving him hard time, so he shrunk his penis by half. Aside from that, his day continued as usual.

The school was over and John walked home. When he came home he spotted his sister's schoolbag is already there. He also noticed a pair of men's boots. "My sister has a boyfriend's visit."

He heads for his room. He knows when his sister has a boyfriend over, they use to make noises. As he is about to open his room's door, he hears a loud moan coming from inside her room. He freezes for a second and moves forward to her room. He spots her doors are not fully closed, leaving him a space to look inside her room. And there he spots them. Both of them were naked in a sexual act you had never seen before. Eric standing on all fours and facing upwards at Kate. She's standing over him holding her massive black cock and pushing it slowly into Eric's mouth.

"Oh! I love when you struggle to take my tip into your small mouth. We need to train you more." Said Kate with a grin on her face. Eric with a mouth full of her dick just mumbled something in an approval manner.

John peeking into the room just smiled over Eric's misery. The App really made him into sucking a girl's black cock and his hard erect penis just clarified he loves it. John compared their penises - Eric's pretty average penis looked so small next to his sister's monster cock. She could be three to four times the length and girth of Eric. 'It sucks having a smaller dick than your girlfriend', laughed John. But he soon realized she is much bigger than him.

"Your mouth feels so good. I'm gonna blast soon. Prepare for a facial, my love." She removes her dick from his mouth and with a few strokes she starts pumping a huge amount of cum all over Eric's face. Soon his head is almost fully covered in a sticky white mess.

John slowly closes a door and leaves them alone to clean up.