He does something for Rias!

"...you know what? Sit on the opposite couch and spread your legs," Issei ordered Rias.

"Of course, Master," Rias nodded eagerly, expecting Issei to fuck her. She walked over, making sure to sway her ass. Once she was seated, she spread her legs, and noticed Akeno staring at her snatch. "...what? You've seen my wet cunt before," she teased, and Akeno smirked.

"Yeah, but this is the first time you've ever put it on such lewd display," Akeno noted. Rias nodded, accepting the explanation as Issei approached.

"Don't move," he ordered. Then, to her surprise, he dropped onto his knees and reached forward a bit hesitantly, and began tracing her folds and her pubic mound with a finger.

"Mmm, exploring my pussy by touch, Master?" she crooned.

"...not exactly," he replied, nervous, but set on his current course of action. He then leaned forward, and extended his tongue, licking her entrance.

"Ah! Master, what are you doing?" Rias gasped, though she couldn't say she didn't like it.

"What does it look like, I'm giving my genie pleasure," he replied, continuing to lick.

"Ah, oh... But giving you pleasure is MY job," Rias protested weakly, but didn't move beyond a bit of squirming, as per his order.

"Actually, last I checked, your job is to give me sexual fulfillment... being able to pleasure my partner is very fulfilling, so just relax, and let me make you cum," Issei stated with a smile before getting back to it.

Rias obliged, relaxing as he had gently but firmly commanded. She let him continue, her heart racing, her face full of eagerness at receiving cunnilingus from her Master. She had momentarily been concerned about the dynamic of this, as she wanted to be the submissive one, but no, this wasn't about her Master submitting to her. He was still very much in charge. And while she still preferred giving Issei a blowjob, she didn't mind this.

Issei continued his attentions, sliding his tongue into her entrance, and wriggling it around. He was pleasantly surprised by the flavor of her nether regions. He was expecting something more salty or acidic, but it tasted sweet, almost fruity, though he couldn't place what fruit it most resembled. He supposed this was because she was a genie. Though he wouldn't be surprised if her being a Devil was the reason. He wouldn't know until he either asked, or tried it with another Devil. Regardless, he kept going, caressing her pubic mound with his fingers, appreciating the smooth feel.

His attentions were a bit on the clumsy side, his inexperience on display, but he made up for it with vigorous enthusiasm, and determination to improve. Eventually, his focus shifted to her clitoris. The cute, hypersensitive little nub captured his interest as he withdrew his tongue from her folds, replacing it with three fingers. "Oh!" Rias gasped as Issei did this, followed by starting to lick her little happy button. "Yes, please, Master, more!"

Issei didn't need telling twice, growing more and more confident with each lick, and working his fingers in and out of her and going at it vigorously. Rias kept squirming as much as she felt was allowed, given his order to stay still. She refrained from bucking her hips as she rapidly approached her release. "Master... I'm almost there..." Those words spurred Issei on, and he redoubled his efforts. "Unh!" Rias moaned.

"...wow, this is hot," Akeno crooned, cupping her own boobs through her uniform, impressed that Issei was willing to go down on a girl despite being the one in control.

Rias screamed and her back arched as she came hard. She covered her own mouth to try to keep any of the other students doing club activities in the building from possibly hearing. She the released the tension in her body, leaning back into the couch. "...did you like that?" he asked.

"... you're a bit inexperienced, Master, and at the end of the day, I prefer giving you pleasure, but yeah, I do love that you did that," Rias nodded happily.