On her back.

Kenji stared Shoko's ass rippling with each hard thrust it was absorbing. He wanted to keep plowing the gorgeous doctor's unbelievably tight pussy but his balls needed to release its load. He assumed she was on a birth control pill but he did not want to risk getting her pregnant despite the very small chance -- his wife was only one woman he wanted to impregnate. Pushing her away, Kenji pulled out just in time with the first jet of cum splattering across her back. He gripped his cock, trying to control it like high pressure hose as a stream of semen coated Shoko's ass and butt.

"I see you can ejaculate in this position, Mr. Kataoka," Shoko panted, looking over her shoulder to see him stroking his shaft to squeeze the last drop of cum from his balls.

"Yes, doctor," Kenji smiled at his handiwork. Shoko, her smooth skin glistened with sweat and plastered with sticky jizz, held on to the chair for support with her knees visibly wobbling from the merciless pounding he gave her. He grabbed some paper towel from the cupboard and considerately wiped the white goo off of her body.

After catching her breath, Shoko turned over to sit on the chair and let out a gasp. She stared at his huge cock, still hard and erect despite three releases. No patient of hers has had such stamina like his before! She wanted to test his limit.

"Are we done, doctor?" he asked timidly, sensing her eyes on his erection, slick with cum and pussy juices.

"No, Mr. Kataoka," she smiled mischievously. "There are still other positions that I would like to test to see if you can ejaculate in."

"Yes, doctor," Kenji bowed his head slightly as his cock twitched at the thought of fucking the gorgeous doctor again and again.