They keep it a secret for the sake of their subjects.
Lord Aizen can do what he wants, of course. No one would argue that. Lord Aizen rules largely through fear, however, and it might shake the very foundations of Hueco Mundo were he to be seen in these moments of tenderness.
It's more fun like this, anyway. Keeping it a secret adds a thrill to it - a certain urgency, a delicious sense of sin. Imagining they might be caught at any second - pretending it would matter.
Gin lies beside Aizen, stretched out with his arm behind his head. He's as naked as the day he was born - assuming he was born, and hadn't called himself out of nothingness through sheer will and the desire to ruin someone's day - and his eyes are closed. His eyes are always closed. Tousen might be blind; Gin just doesn't need to see.
Aizen, propped up on an elbow, reaches with his free hand to stroke his partner's flaccid cock. It responds immediately, blood flowing to Gin's nethers to leave it swollen, stiffened, and flushed with colour. It's really the only time there is colour in Gin. He's an incarnation of winter, the thick blanket of snow that conceals a barely-frozen lake - a sense of danger with no visible reason why.
Toshiro Hitsugaya, eat your heart out.
Gin stirs, a feline grin crawling across his mouth. It's Cheshire-sweet, too saccharine and too wide. His hips rock up, though only barely. He can't be bothered to do anything more. The pad of Aizen's thumb trails along his cock, a feather-light tease. It causes the rod to twitch, belying that seeming disinterest.
Aizen's found a crack in the white armour and takes full advantage of it. His hand curls loosely, embracing the shaft, and like a dancer on a pole, rides it up and down. There's just enough contact that skin slides over muscle, bunching subtly toward the head and snapping back as soon as it's allowed. Gin exhales at length, his back arching a little more. The head of his cock displays an angry violet-red, but there's no rage in the man himself - only a hungry contentment, eager to be sated entirely by his lover's touch. Today, Aizen is willing to let him have it. Tomorrow - who knows.
Theirs is not a traditional love. Such emotions are for lesser beings, base and without control. Still, there's an affection between them, a sort of genuine fondness - an incestuous brotherhood born of the sword. They've fought side by side and each had the other's back - as well as every other part. Gin will never worship at Aizen's godly throne, of course. That's no secret. He might stand beside it, behind it, even sprawl across it, but he'll never kneel before it. There's no room for another deity in Aizen's pantheon, but Gin's earned a place there none-the-less. This is but a fraction of his reward.
Aizen knows the end is coming when Gin's cock grows a little larger, a little stiffer, in his grasp. It's not a violent end, the sort so many said they'd meet, but a gentle passing. White dribbles from the slit in the fleshy tip, leaving Aizen's fingers wet as if with melting snow. He brings his hand to Gin's mouth and lets Gin taste himself, then claims the tainted lips for his own.
Everyone knows about Aizen and Gin. They don't let on because it's safer to leave the lords with their illusions. Those are men with hearts of ice, who melt only for each other, and no one wants to be in the way of the shards when they shatter.
Author's Notes: Written for Porn Battle Round Ten @ IJ. The prompt was Bleach, Aizen/Gin, our litle secret.