Rias lectures Issei, then they run into the Stray!

"...so, I already told you that there was a dead lock between the three factions, right?" Rias asked Issei who nodded, before blushing as she gently grabbed his hand and guided it to her ass. Getting the hint, he started groping it through her skirt. "Right now, there's an uneasy truce between us, but before then, we endured a great war, and all sides took enough casualties that we agreed to a truce."

"Right, you guys got sick of the bloodshed, so now you're more in a cold war than an all out one?" Issei asked, giving her rear a squeeze, and making her moan.

"That's more or less accurate," Rias nodded. "Of course, the Devils didn't have enough numbers remaining to maintain our society, so we created the Evil Piece system. A means of replenishing our numbers by remaking humans into Devils."

"Right, you're the King, Akeno the Queen, Kiba a Knight, Koneko a Rook, and myself a Pawn," Issei nodded as they checked another room. No Stray there. "...so, you lack a Bishop then?"

"No, we have Gasper, but he's... Inactive. You'll meet him eventually," Rias replied, looking a bit uncomfortable, so Issei decided against pressing for details.

He nodded, and asked, "So... I found out already that Koneko has superhuman strength from her Rook piece, does that mean all pieces have their own benefits?"

Rias beamed at him. "That's correct, and I'm glad you asked that! It's an astute question!"

Koneko snorted. "It's an obvious one, it just proves he's not a total moron," she replied, and Akeno gave her a look.

"It actually proves he's smart enough to actually ask questions and try to figure things out instead of just waiting for all the answers. It's a basic part of critical thinking," she chided Koneko, who huffed.

"So, what benefits does being a Pawn offer?" Issei asked, before they opened a door, and froze as they saw a monstrous figure in the shadows.

"...for now, let's just say there's a reason I want you to to observe how other pieces fight," Rias remarked as he took his hand off of her butt. "It's invaluable for a Pawn to know such things..."