She is a very eager submissive!

"Wow... um, so..." she blushed and glanced away.

"You want to go ahead and be a total sex slave along with me, don't you?" Rias grinned, leaning in. "You've got that strong sense of submissiveness and compersion to you..."

Asia nodded, flushing even more deeply. "...yeah, I do... and I want to ensure Issei's really happy... and I think I'm much more perverted than I thought..."

"Repression for years can do that to you... how much control do you want Master to have over you?" Rias asked her.

"...close to total," Asia admitted. "Nothing that conflicts with my morals... which are now about whether or not I would actually cause unwarranted harm to someone if I obeyed Issei," she added with a flush. "And... maybe something kinky? Like something that would show Issei that he owns me?"

"Oh! I like the way you think!" Rias grinned, before turning towards Issei. "How about a collar? One that compels her to obey you, and rewards her with pleasure each time?"

Issei flushed, and he imagined Asia in several different kinds, before settling on one idea. "Rias, I wish for Asia to have a gold collar that is encrusted with an emerald that matches her eyes, and enchanted to compel obedience, within limits she herself will decide, and give her positve reinforcement every time she does obey."

"Your wish is my command!" Rias clicked her fingers, beaming at Asia, who gasped as the air around her neck glowed, before manifesting into the collar. "Aren't you just adorable in that?" Rias squeed and hugged the blushing, but smiling Asia. "Now then, let's get you naked and ready for Master!" she gushed, immediately getting Asia out of her nun outfit.