She does, and it is!

Rias then noticed a slight smudge on the lamp, and gave it a quick rub over with her arm. Suddenly it jolted, and expelled glittering red mist at her. "Ack!" she yelped, dropping it, and tring to back away, but it turned out the vapors were solid whenever they wanted to be, and once she was enveloped, she didn't get far, and she was lifted into the air. "Hey! Put me down!" she protested, before some of the mist covered her mouth to keep her from making too much noise. Issei on the bed stirred slightly, but otherwise showed no signs he was conscious enough to even try to come to her aid.

Rias struggled, before pausing as the mist seemed to caress her body in a rather pleasant manner. She paused as she heard a voice in her mind. An Eldritch presence, but not hostile. Most wouldn't understand it immediately, but Rias was a Pure Devil, and as such, she got the gist of what it was telling her. "Do not fear. You will enjoy this immensely. Relax, as you ascend to a higher state of being at a price you will gladly pay when this is done."

She moaned in pleasure as she felt the mist sink into her body, it didn't change much. Kind of hard to improve on perfection after all. At most, it added a few centimeters to her breast size, and almost unnoticeably flared her hips. It did also ensure she didn't grow any hair on her face or below the neck as well.

She felt the knowledge of what was happening, and a gentle, pleasant nudge towards submission in her mind. Nothing forceful, she could resist it if she wanted to... But her capacity for pleasure was expanding, and the suggestions came with an incredible sense of well being that made her reject the idea of fighting it. Normally, she would be against being sexually enslaved, but this magical process made her feel just how good and fulfilling it would be to accept this.

It was just too good to refuse. "Yes, please, make me this Sex Genie..." she moaned quietly. The mists began to form into silk, Arabian style harem garb on her body. Red, transparent, and extremely soft, a crop top with gold trim formed on her chest, her midriff and some cleavage left bare. A skimpy set of silk panties were added, along with a red silk loincloth, also with gold trim. Then came a veil over her lower face, attached to a circlet.

Gold armbands formed on her wrists, along with detached sleeves to the harem outfit, attached to gold armbands instead of the body of the silk outfit. She also gained a golden collar with some encrusted rubies, and gold anklets. Then came the final, most pleasant and arousing part of the transformation, which Rias had anticipated due to her ability to translate the intent of the Lamp.

Her feet, starting at her toes, melted away, diffused into the mist. The effect climbed all the way up to her waist, before it stopped. The mist withdrew from her body, being absorbed into a wispy tail beneath her, connected to the spout of the lamp, leaving her floating in the air, caressing herself. "Unh, wow..." she crooned.

She then felt the pull on her being, and looked down to see the Lamp, and how she was being drawn into it. She didn't resist, merely serenely closed her eyes as she allowed herself to be pulled within it.