You persuade him

You stand in front of Jake when he is trying to leave in a hurry. He is a head taller and looks like he just wants to push you aside but he knows better.

With an innocent smile you tell him you want to test the device with him. He finds your fit body very attractive but wants no part in a painful session so he respectfully declines.

When he is trying to walk around you you put your small hands on his chest and changing to a dominant tone you explain "You have 2 options. I can accuse you of being disrespectful, even of touching me and have you sentenced to the device which will make me very angry and mean or you can accept voluntarily and I'll go a little easier on you, don't get me wrong, it will be very painful but I will try to avoid any permanent damage. Your choice".

Jake knew that in this feminist institution, she had all the cards and had him at her mercy so reluctantly he complied.

Ana tied his ankles and wrists to the X shaped frame and only when he was totally secured she eye his crotch appreciatively. The regulation very tight pants left his considerable bulge protruding invitingly. Even though she had never done this in public before, she decided to go all the way and do him exposed. As soon as she lowered his zipper, his considerable manhood spilled free. It was her first time seeing him naked and it was a pleasant surprise. He had a nice and thick uncut cock that even limp had a decent size. His balls were even more impressive. She loved everything she saw but to avoid distractions and keep this a strictly painful exchange she, with effort, tuck his penis back inside, leaving just his huge balls hanging exposed.

To make his humiliation worse the teacher and a few students were still hanging around but Jake could only watch in despair and hope she kept her promise of preserving the integrity of his manhood while she kicked off her shoes and removed her socks.

Looking at her perfect legs, her super short skirt complemented so well, he got ready to receive her white foot in his sac but she first had a demand to make. Ana got closed but spoke loud for all the other women to hear "I signed up for self-defense training as an extracurricular activity and I need a sparring partner." Before continuing she casually took hold of his left naked ball with her right hand. It was a firm but not crushing grasp but he knew that could change very quickly. "Will you be my partner?".

Jake knew that meant endless afternoons of testicular pain and hesitated only to find her left hand join in grasping his other nut.

Ana loved how each of his testis was big enough to fill one of her hands and for effect increase the pressure just a little extra notch. The response was immediate.

"Sure, I will" he quickly replied. Ana looked over her shoulder at her teacher and she answer "That is good enough as a commitment, I'll make sure his voluntary offer is accepted".

Ana turned to face him again and took a delicate step back. None of the other females moved an inch. They were clearly going to stay for the show.

This time Jake's fears became true when Ana introduced her perfect right foot to his naked balls. He was not anticipating the level of pain he felt. She was fit but slender and had a delicate beauty that made her look more like a girl who would slap you in the face instead of hitting you in the balls. But looks can be deceiving and this girl has an older brother which allowed for much practice growing up.

His balls were still bouncing in all directions when her second kick landed. She was lining up a third when the girls began cheering and the teacher exclaimed "It is great how he can't move at all!". All the girls agreed and that gave Anna an idea.

Lifting her leg slowly she took her sexy foot all the way up to the base of his loose scrotum. Jake was hyperventilating with his eyes closed, as if not seeing her kick him could make the pain more tolerable. When he felt her cold skin of his manbag he flinched but then opened his eyes in surprise when the pain did not come.

While tenderly lifting his nuts one inch Ana told him "I'll give you a chance to duck my kicks and for that, I'll count to 3. When I get to 3 my foot will hit you, ok?"

He nodded and swallowed hard. Ana lowered her foot to the floor and started counting. Her foot collided with his weakest spot right on 3 but Jake even with this advantage could not move an inch because of the restraints and took the blow in the center of his very full scrotum. She repeated this over and over. Everyone could see how knowing when the blow was going to land added another layer of agony to his already terrible situation.

When he told him she was tired of kicking him he relaxed a little, thinking he was going to be released or at least get a break but instead of taking a break, Ana put her hands on his shoulders and told him "Did I ever told you my brother says knees are my best blows? Well I think he actually says worst but soon you'll know what he means".

Jake like any guy had been kneed a couple of times. It was the quick response by a girl you upset but they had been half-hearten blows to the general area of his clothed groin, more meant to intimidate than to hurt.

Ana was about to change what he considered a knee to the groin forever.

They all could see the very pretty redhead grabbing his lapels for control and dealing the much bigger boy with a flawless knee.

This was the quintessential lady's blow and she did it with as much elegance and economy of movements as can be achieved but without losing power or precision. It was quick, violent, and the type that comes as much from below as from the front, not leaving any avenue of escape for the delicate dangling organs.

The effect on his side was dramatic, making clear her terrible effectiveness. If they could watch a slow-motion repetition the ladies present could have appreciated she only took half a step back with her right foot and almost didn't move her upper body but her leg became a blur. Being used to hitting her moving brother it was easy for Ana to guide her knee precisely into his testicles at top speed while avoiding to even brace his thighs. The almost unstoppable momentum of her knee bone against his softer testicular tissue put him on the verge of castration.

He lost all control and would have fell to the ground as a sack of potatoes without the support of the restraining device.

Ana's audience exploded in applause. Nobody had ever seen a knee like that.