Sometimes
Sometimes they did this.
When they kissed it was when everyone else was gone, in a mission, speaking to their master, dull and tired and hollow duties (how fitting, for people so hollow). Aizen's eyes were everywhere, they knew, and they tried secluded areas; the dead trees, the little caves, the empty awfulness, just as Ulquiorra himself felt empty, just as Grimmjow himself felt angry and lacking in purpose.
When they hid they would speak little, and Grimmjow had a tendency to start first- he never did the nibble in the ear thing- too affectionate and trite, but aimed immediately into mashing his mouth at his fellow Espada. No softness, no wooing, no cute "sweet nothings" that humans tended to indulge in like the pathetic fuckers they were. Ulquiorra never returned the kiss so much as wildly went at the other's tongue with something that resembled hunger, though what he was hungry for, he didn't say. Grimmjow didn't ask.
They were both very hollow, and outside of Aizen's orders it was brutal waiting- hell the shinigami were excitement for them, but that wasn't the two's immediate concern at the moment. They both knew their "meeting times" would be less frequent, and they didn't know whether to be relieved (for this was unnatural in itself, their every so often retreats) or disappointed.
They had yet to fuck, and that was fine for both of them, because neither was willing to bottom. Grimmjow would call it a "honeymoon" sometimes after they would "fiddle" and "diddle" and "dick around" (his words too, he could be clever if he wanted) and Ulquiorra would retort, "There's nothing sweet about this, no honey, no moon" and they would forget their words as their bodies explored each other like they were trying to find something in the folds of their skin that they could not find within themselves.
It was hollow, like everything else they did.
"So what's your obsession with hearts anyway?" Grimmjow asked him one day, one of their last meetings.
"I envy how stupid humans are," Ulquiorra replied at last. "Love is a privilege. We play with each other because we're bored and empty. They play with each other because they think they feel something."
"That shit's overrated," the sexta told him.
"Maybe."
Grimmjow knew he was being used, in a funny sort of way that Ulquiorra did, because the smaller of the two wanted to feel something, and was curious enough to see if love was something he too could feel. And Grimmjow certainly didn't mind, because it felt good, but could not help but feel- what was that? Cheated? Regretful? Wanting?
Nah.
"Well," the taller said, "What DO you feel?"
"Nothing."
Same old same old, Grimmjow thought, with a brief tugging at his chest that he stifled and suffocated to death.