The secret of Kunimi-Yamas success

It took almost 20 minutes for the door to open. Umiko came out alone. Her clothes were complete again. Well, almost complete. I could see she was not wearing a bra anymore. Her nipples clearly pinched through the white fabric. A purse hung loosely over Umiko's shoulder.
Umiko took a deep breath. "Do you know why the Kunimi-yama is so successful?"
"Not really, I've heard that a new kind of teaching concept is being tested here."
"New kind is not quite right. It's just been extended two years ago, I'll explain it to you, just follow me." Umiko took me to a classroom. "Professor Watanabe discovered eight years ago that schoolgirls achieve much better learning outcomes when rewarded by sexual stimulation. She has developed special classroom equipment, but so far Watanabe's methods could only be applied to schoolgirls. Have a look at this school desk here."
The design looked similar to the chairs I knew from American high schools. On the left side a writing desk was attached. However, this was bigger and had some rotary switches at the top. The seat was of dark wood, with a ridge, about two fingers wide in the middle, with two holes behind each other. Left and right of the ridge several metal contacts were embedded in the wood.
"Unfortunately, I can not show you how the Watanabe Desk works, it needs to be unlocked by the teacher." I could imagine how the bank worked.
"Up to now there was no way to construct a Watanabe Desk for Males, that's why Kunimi-yama has been a mere girls' school. The lust girls make sure that we're happy even when we do not have lessons. To make it possible for boys, to profit from Watanabe's methods, some lust girls have been trained to cater to the needs of male students. "
Umiko reached into her schoolbag. The red collar that I had seen around Kohar's throat came to light. "She's yours now. If you accept her, I'll explain a few things to you."
Behind us Koharu entered the room with lowered eyes ...