Fittingly enough, missionary!

"So..." Asia flushed, sitting naked, save for her collar, and her panties, which Rias was currently pulling down her legs. "What position do you want me in, Master?" Asia asked, tasting the word, and finding she enjoyed calling Issei that.

"If I may make a suggestion, Master?" Rias cut in. "Missionary. Which I normally consider the most boring position, but the irony of it this time around more than makes up for it! And besides, even missionary is fun, the "least" fun form of sex is still incredibly titilating!"

"...I like that idea," Issei agreed, and Asia, not needing any further cues, leaned back, and only briefly hesitated, before parting her thighs.

"...I'm ready..." she said softly, watching as Issei unzipped his pants, and pulled out his erection, and approached her, stepping between her smooth legs, and gazing at her glistening nether petals. "...put it in me..."

"This is your first time, so I'll take it slow," Issei told her, placing the tip of his one eyed serpent at the entrance to her burrow, and slowly pressing in. He held her hips, and held her steady as he entered her, carful not to tear her hymen. Contrary to popular belief, the hymen wasn't a barrier, so didn't need to break for sex to happen.

"Ah!" she gasped, arching her back. "Oh my God, this is amazing!" she gasped, before bracing herself, and blinking when she realized that her head didn't hurt.

"Master wished that exclamations like that during sex didn't count for us early on, no need to worry," Rias teased as Issei bottomed out in Asia. He waited several moments, before he started to move slowly.

"Ah! Unh!" Asia gasped, her nether lips holding onto Issei's member like an embrace. "Oh... I never realized sex could feel this good!"

"That's the point, it's an incentive for procreation... though you don't need to worry about that, Rias's magic will ensure that you won't get pregnant..." Issei panted, continuing to thrust his hips back and forth in her, leaning down slightly, and placing his hands on the bed on either side of Asia's head.

"Mmnh... okay," she nodded, gazing up into his eyes. He met her gaze, losing himself in not only the pleasure, but the soft glint of the emerald orbs before him. "Faster..." she gasped out after a bit. He nodded, obliging her, and before long, was pounding into her, his hips smacking against hers with every thrust. By this point, she had asjusted, so didn't suffer more than a slight ache from the pace.

"Unh, this feels great..." Issei grunted, Asia nodding in agreement.

"Master, I... I feel some kind of... pressure building..." Asia panted out, and Issei nodded.

"That's an orgasm, Asia. Let it happen," he grunted out, his own organ beginning to pulse and swell. Then, with a loud cry, his nut busted, flowing into her.

She gave a loud exclamation of pleasure as her eyes widened, her back arching more as her hands clenched into fists. Issei held his shaft in her fully for several moments, until it finished releasing his seed, and he pulled out, and slowly lowered himself atop her, collapsing gently, and pressing their sweat glistened bodies together. "...wow," she wheezed, before holding him close and kissing him, a gesture he eagerly returned.