Family structure:
- Father: NAME_1, 43, balding, beer belly.
- Mother: NAME_2, 35, nice figure and rack.
- Son: NAME_3, 15, nerdy, dark greasy hair, unfit, shy, horny and creepy.
- Daughter: NAME_4, 13, pretty, blonde, slim, cute and girly.

Smutty and kinky story prompt, make it long and open ended without a conclusion: One evening NAME_4 asks her mom about sex in general and masturbation in particular. She is curious and wants NAME_2 to explain how to do it and how it feels.
NAME_2 agrees to a training session of sorts in NAME_4's room. NAME_2 insists on letting NAME_4's brother be part of it so she doesn't have to explain it twice. She calls NAME_3 into NAME_4's room while NAME_4 and NAME_2 are getting undressed.
First NAME_2 shows on NAME_4's bed how she does it, showing and explaining everything. NAME_2 then shows it on NAME_4 until NAME_4 takes over herself.
Meanwhile NAME_3 is silently standing pantsless next to the bed and slowly masturbating, taking in the sight of mom and sis naked, their legs spread in front of him. He cums on his little sister's small boobs and cute face.
NAME_3 discreetly films the scene with his phone to enjoy later.