Quite disbelieving, but Rias starts with the Devil stuff!

"Well, Master," Rias grinned as she crossed her arms under her ample bust. It has the desired effect of drawing Issei's gaze to it. "To start, you're no longer human. Rather, you are a Devil now."

Issei, staring at Rias, mostly her boobs, blinked and said, "Uh... What?"

"See, you straight up died to a Fallen Angel, the one that posed as your girlfriend. You were seen as a threat due to a Sacred Gear you possess," Rias explained, gazing down to where Issei's arm was.

Of course, given that he was still covering his crotch, he drew the wrong conclusion. "Wait, you mean my dick? I know it's a fine specimen, but my manhood isn't a threat to anything but the virginities of lovely girls!"

Rias blinked, before she burst out laughing. "No, Master, not your wonderful cock! Though I do think it's very nice!" Of course, as his Sex Genie ****, she would have a bias, but that was neither here nor there. "It's in your hand! Your left one to be specific!"

Issei blinked and looked at his left hand. "What's a Sacred Gear?" he then asked Rias.

"Items that were forged by God," Rias replied with a smile. "Essentially, some humans are born with them. They're a part of your very being. They grant special abilities. Indeed, many of the most famous people you have heard of? A good number of them likely had a Sacred Gear."

She then showed Issei how to manifest his, though it led to him taking a silly pose from a manga he had read when he focused. Rias did not criticize. Instead, she took the opportunity to visually drink in his cock once both hands were off it it. She loved gazing upon her Master's manhood.

He yelped as the red gauntlet formed on his arm. "Whoah!"

"See, Master?" Rias grinned, floating around behind him and massaging his shoulders. "At any rate, because you were killed, you made a dying wish of sorts. To die in the arms of a beautiful girl. A more common thing than you might think. I noticed that you had a Sacred Gear, so I decided to resurrect you as a member of my peerage. You are a Reincarnated Devil now."

"...I see," he remarked, still gazing at his arm, and making Rias pout slightly. She slightly regretted showing him that, it kept him from looking at her, damn it!

She floated back into his view, and was gratified to see his gaze drawn back to her. She then continued to explain about Devils and Fallen Angels, and the political system. "As for Peerages, they're essentially a group of Devils, with chess piece themes. As the King of my peerage, I have authority over the others in the peerage."

"Okay... But what about the genie situation you got going on?" Issei questioned. "And if you're the King, why call me Master?"