Project Maneki IV: Private Dancer
Ryuuji figured the easiest way to get DNA matter was to date the girls, then find something that would have their DNA to bring back.

First on his list was Mako. He barely knew her as the spike haired girl in Biology class, but a brief glance in her direction quickly established her as having the biggest bust in the immediate vicinity. After lab, he stepped in front of her as she passed by.

"There's a new place opening up near campus," he proposed.
"I have rhythmic gymnastic practice after class."
"I'll wait."

He had no idea she had held a crush on him for some time.

In the empty gym, Mako motioned for Ryuji to sit down. "Oh, and let me have your belt."
Ryuji obliged.
Mako did her ribbon dance routine, using Ryuji's belt the best she could. She would have preferred a tie. 
He looked amused but not overly interested.
"And this is my rope routine." Mako stripped to her panties and bra. Her heart pounding, she did her routine in ways she never had even imagined, exaggerating her moves, so her audience of one saw every part of her. She made sure her finish was only a few feet from him, panting madly, legs askew.
"Now that was something." Ryuji was paying attention.
She had seen that great swimmer's body before, at the meet. It was time to see it again.
She stood up. He stood up. She noticed as they kissed, his hands went immediately to her ass. She tugged his belt-less pants to his knees. As she took him in her mouth, he beamed down in approval.

As the light dimmed in the windows, he scooped up her socks and placed them in his pocket. As he moved towards the door to leave, he heard her call out.
"Did I wear my socks here?"
"To be honest," he lied. "I didn't see them."