"Emily, for as far back as you can remember, you have always been deeply aroused..."
You hesitated a moment to savor the possibilities, "by everything." You finish, grinning widely.
Emily's eyes widened at your openly revealing her secret. "What?! I don't... ugh!" she blushed furiously and sat down on her bed, crossing her arms in front of herself defensively.
"It's not exactly something you could ever hide." you say with a smirk. "I mean, literally everything seems to turn you on, even the most mundane things... I'm sure your friends know about it too..." You added, watching her blush deepen, realizing that you weren't lying. She didn't realize that it was the veil that had made this all true. This was how she had always remembered things; she had no clue this was her brother's doing.
Emily looked down at herself, knowing full well that what he said was true. Her body responded to literally everything with a wet warmth between her thighs, at minimum. When she was younger, she had believed it to be normal, just part of puberty and growing up. But as she had confided in her friends, she learned that this was, in fact, anything but normal. Everything, no matter how perverse or mundane, seemed to turn her on. It seemed that the only thing that helped was desensitization: as she was exposed to something more and more, it would become less sexually exciting to her. This was only a small consolation, as there were always new things, new ideas, and new fetishes to discover and explore.
She looked at you with pleading eyes. "You... You can't tell anyone..." she whimpered, feeling her body responding already just thinking about what you could do if you decided to share it with others.
"Don't worry Emily." you said, trying not to laugh too hard. "Your little secret is safe with me... For now at least." You couldn't help but grin wider as she paled at the implication. "Now go ahead and shower yourself in front of me, I want to see my cute sister's body get wet."
Emily blushed furiously. Having worked hard to hide this from her brother, they had never done sexual things together, but now that he was literally asking for it? And blackmailing her to boot? It would be nearly impossible for her to control herself from the intense arousal she felt even just thinking about incest.
"You... you can't be serious!" she whined, looking around as if someone could save her, but no one was home and you knew it full well. "Please don't make me..." She pleaded, but deep inside, a part of her was already getting wet at the thought of what would happen next...
"Oh, I won't make you. I'm sure your desires will guide you all on their own." You chuckled as she gulped hard and closed her eyes, trying to fight it off. Her body betrayed her though, her nipples standing erect through the fabric of her t-shirt, clearly showing how much she wanted this, despite her reluctance.
"But... but..." She stuttered as you approached her, grabbing her by the wrist and guiding it down to feel her soaked panties. "See? You're already wet for me."
Her face turned redder than a tomato, her heart racing as she reluctantly undressed in front of your hungry eyes, exposing herself completely nude under the dim light of her bedroom lamp. She tried to cover herself with her hands at first but soon gave up on this futile attempt and started to slowly rubbing her breasts and between her legs, moaning softly as she did so. "Oh... Oh god."
You couldn't believe your luck: Your little sister was standing naked in front of you, playing with herself shamelessly while you watched, all thanks to the power of this Veil. You felt yourself getting hard at her show and decided to help her along a bit more. "You want me to join you?"
She blushed even further, as she couldn't honestly deny that she wanted it so badly...