Asuka does it like she has something to prove, like if she grasps Rei's breast the right way, or makes the right sounds, some invisible arbiter will appear to clap his hands and shout "congratulations" and give her ownership of the universe forever and ever.
Rei doesn't have anything to lose, or, for that matter, anything to do. She doesn't feel aroused the way a normal person does (if any of them are really normal), but she knows enough to cant her hips the right way and grind. Her shoulder blades itch when she's around Asuka, as if she's provoking some part of Rei that she's kept sealed deep beneath.
It infuriates Rei. It's completely different from how she relates to Shinji, wordless gazes and stammering and trying not to hurt each other more than they already are. Trying their best to approximate emotions they aren't even sure they feel.
Asuka has the gift of drawing out Rei's emotions. With her, everything is loud and clear and simple and wrong.
Rei's cold fingers stretch Asuka's slit out, methodically, and Asuka snorts about how she's just like a puppet, and Rei's vision is flooded with red. The red of Asuka's hair, the red of her anger, the red of the parallel scratches down her thighs. She hates red.
She drives her fingers inside Asuka in a ramming gesture, not even bothering with subtlety anymore, and Asuka shrieks, tossing her head back. It might be joy or anger, she can't tell.
"Now that's more like it, you damned doll! Come on, you bitch!"
Definitely joy, then. Rei moves up slowly, removing her fingers from Asuka, and Asuka doesn't even have the courtesy of pretending that she's affected.
She wipes her hand on Asuka's hair, then slaps her across the face.
Rei's hand stings from the impact, but Asuka laughs and laughs and laughs, rubbing her cheek gently like she's just been caressed by a lover. Her lips open, ready to spit out a curse, or ready to draw Rei closer for a sloppy, biting kiss, and Rei isn't sure which one she hates more.
Rei's panting, kneeling on the bed like a supplicant to a goddess, and she doesn't know how to wound Asuka more than Asuka's already wounded, but she's determined to find out.
Anger and hatred are roiling in her, making her feel sick, the iron tang of blood in her mouth.
Rei's actually feeling something.
She supposes it's Asuka's gift.
(In German, gift means poison.)