This isn't what she wants, this isn't what she needs, and this isn't what she's ever imagined for herself. But life has often forced Rukia to do that which she least desired, and this will end up no exception to that rule.
Rukia once sacrificed a man she loved to save him from a Hollow; it seems almost fitting of fate to let her now sacrifice herself to do the very same.
---
In the end, Ichigo's Hollow had wanted her. Not power, not glory, not an unlimited source of souls, not even her own soul.
It had wanted her. Just her. Just Rukia... and every single thing Ichigo had wanted from her, directed towards itself. Love, devotion, humor, beauty, carnality... everything, it had assured her, grinning widely, that Ichigo had always hoarded selfishly in his dreams before.
All she has to do was give it all of that, this night, and every night it demanded afterwards, and it had promised to give Ichigo back. Bindingly promised. And once it had done that, there was nothing really left to negotiate, or say, or speak of.
In the end, it had ended up devouring her. It just hadn't done so in the expected fashion.
---
When they finally make it to a bed (she hoisted up in its arms in a cruel parody of bridal tradition as it strode past everyone else, half of their friends' eyes cast down to the ground and the other half following them with something akin to horror), the Hollow places her atop the sagging mattress with something like reverence and breathes his words across her face.
"You'll learn to love me," it manages to whisper in an almost normal fashion, though its disturbing grin still splits its face in away the human Ichigo would never allow. "You'll learn to give me what I want, what he" (the word is spit out like a curse) wants, without any struggle. You'll learn to anything and everything. Watch. I'll make it so. Watch."
There's no time even to spit out a denial before it crouches down besides her and strips down to nothing. Shock renders her mute and beauty renders her still.
---
The Hollow is just as inexperienced as Ichigo would most likely have been. The only real differences between the two (besides those terrible eyes, besides that wicked smile, besides the fact that it has no soul within it) is that the Hollow has no real shame and a stamina that far outstrips that which any 16 year old boy (high powered Shinigami or not) could muster up.
It's adventurous as well, and doesn't let a mere lack of knowledge keep it from kissing, licking, sucking, stroking and (dear god) biting her wherever it pleases. It's equally attuned to what pains and pleasures Rukia and equally good at manipulating both points so that even delight tears her up and her wounds ache with longing afterwards. It discovers soon enough that the nape of her neck, the tips of her breasts and the smooth skin along her inner thighs are her most vulnerable points, and that she cries out most when it closes his eyes and throws back his head and looks just like the other one.
It hates that just as much as she does and always punishes her afterwards.
She doesn't touch it and she doesn't pleasure it back; whatever else she might do, she doesn't allow herself to betray Ichigo in this way. But in the end, she ends up orgasming three times beneath the palm, lips and cock of Ichigo's Hollow. And when Ichigo finally comes back to her, panting and whimpering and choking back ugly noises in his throat, she knows that he sees that as the worst betrayal of all.