Notes:

This is not a pairing yet to my knowledge, not unless Shunsui is involved, but I think they'd be sweet together. Both love books, both love Shunsui and both are generally awesome characters.
Also I do no believe Juushiro would have such a dirty mouth, he's far too much of a gentleman for that.
Beta the lovely: SocialDegenerate /users/SocialDegenerate As always very thankful

The pond by the estate was nearly completely frozen over, with only small pockets of water visible over the ice. Nanao paused for a moment, hands gripping the frosty railing: she'd been sent for by her captain's oldest friend Ukitake, on the orders for a mission no doubt. She enjoyed the white haired captain's company. He was settling and charming in a manner her captain was not, and while his friendship with her was strictly professional, she often enjoyed visiting his family's estate, either in the presence of Kyōrakuor by herself, as was the case now. Breathing in a chilly breath, she turned to approach the door only to be startled by the appearance of the captain himself. Holding her chest in surprise, Nanao sighed dramatically.
"Goodness me Captain, you scared me half to death!" Smiling, the tall man rested a calming hand on the lieutenant's shoulder.
"Sorry, sorry, Lieutenant Ise, the snow muffles sound I suppose." Smiling in return, Nanao gestured to the pond.
"Will your koi be alright? In the ice and cold?" Joining her at the railing, Ukitake looked out over the frozen planes.
"They've survived well enough in previous years: they should be fine, we have some especially large ones this season and so the winter shouldn't bother them."

Moving back toward the estate, Ukitake held out his arm for Nanao to join him. She graciously accepted, and they wandered along the decked path to the courtyard. Ukitake's prize-winning bonsai lined the walls on tiny shelves, all lit with a selection of differently burning candles. The lighting is amazing, Nanao thought as they paused at a small sitting area set with tea and sweet treats. Taking a seat, she gazed at their surroundings with wide eyes: the snow was flicking an array of shades of gold, and she couldn't help but think, it's almost romantic. Perishing the thought, she went about serving tea for herself and her host. She paused at the sight of the small jug to the side of table; peeking inside, her faced twisted. It was milk – like one would have in the living world.
"It's not milk." A humorous tone in Jūshirō's voice informed Nanao he'd been watching her every move well enough to know she was repulsed by the thought of milk with tea. "It's a liquor from the living world called eggnog, I believe it's festive." He smiled warmly, taking the tea she offered him. "Perhaps we could try some later." Raising the jug to her nose, she inhaled the sweet, milky smell: it wasn't unpleasant and indeed it set her taste buds alight. She was a sucker for anything sweet, it was one of her greatest pleasures and weaknesses.
"I'd like that, thank you Captain."

The evening progressed comfortably: the pair chatted at length about the dynamics of the Gotei Thirteen, Ukitake's next up-coming book (which he was convinced would not be as good as the last; she disagreed), Kyōraku's downright lazy ways, and eventually how the eggnog tasted. After her third glass Nanao was convinced it was the devil in liquid form, coming to fill her mind with all manner of foolish nonsense. Ukitake had been describing the new plot twist he planned to institute in a coming chapter, and Nanao should have felt privileged that she was being used as a storyboard, but all she could focus on was the way his stark, brown eyebrows blended so well with the contrast of his face, regardless of the slick waves of white which framed it. Nothing looked out of place on the man: it was as though he'd been perfectly designed, even down the slight physical faults.

Those deep brown eyes were boring into hers, with tiny crows feet at the corners similar to her captain- not only indicating his age but also his enjoyment of smiling and humour. It was an intense gaze and she felt herself compelled by it, probably because he was addressing her.
"Nanao-san, are you alright?" His concern was wasted on her, she was fine, nothing more then a little tipsy; but not that she'd let him know that.
"I'm fine thank you, Captain, just a little tired." She smiled disarmingly, only to have him frown in return.
"Are you sure? It's quite cold out here, we can retire indoors if you'd pre-"
She kissed him.
She leant across the table and kissed him, for no reason. Pulling back swiftly, she went to stand, only to have her hand tugged back gently. Ukitake stood, walking around the table to meet her halfway as she looked away, face blushing furiously. How could she have been so stupid? How easily her control had slipped after a few cups of eggnog.
"Nanao-san." She looked up shyly, unsure of his response: would he treat her like a little girl with a crush? Or like his best friend's surrogate daughter? Instead, she felt a warm pressure upon her own lips. Eyes flying open, she was gifted with an image of closed eyes, a wistful look upon his face as he kissed her. Kissing back, she felt his hand reach out and bring her closer in an embrace. A hot brush of his tongue was her complete undoing, and she nearly jumped him. Letting her arms wrap around his neck, bringing them closer together, he slid his hands down to her hips, gently rocking her back and forth as they playfully battled with lips and tongues.

The alcohol streaming through his veins was making Jūshirō bold, or maybe it was simply all of his bottled-up feelings finally coming to light. He'd admired Nanao Ise for years, not only as a ranked shinigami, or for her ability to actually force Shunsui to work, but more so for her elegance and kindness. Her hard work often went unrewarded, especially with her captain's grand nature, but he'd admired it and had always wanted to reward it. But how could he: for all he'd known she thought of him as an estranged uncle, an elder figure rather then someone she'd wish to take as a lover. But now things had changed; as she sucked his bottom lip a low moan chorused from his being, and it was certain that she didn't think of him that way. Feeling bold as brass, he kissed her hard, taking her face in his hands as he licked his tongue along the seam of her lips, relishing the feeling as her entire body arched against him for more.
"Be careful Nanao-san, you might get your panties wet." Even as the words left his mouth, he immediately regretted them. That just sounded...depraved, and if he'd had a chance he'd blown it now.

"I'm not wearing any panties," she purred, watching his large brown eyes widen in surprise.
"Oh..." he said, gracefully depositing her into his lap as he sat, creeping a hand up her thigh, a hot tongue assaulting the sensitive skin behind her ear. "The textile bandit strikes again." Laughing at his own joke, he parted the thick layers of cloth around her waist, dipping his hand in deep until he reach the scalding heat at the apex of her thighs. For a worrying moment, he feared his hands would be too cold, chilled from the outdoors, but as he ran a finger through her moist heat she shivered against him, her hand wrapping in his shock of white hair.
"Oh, that tickles," she giggled slightly, turning her head to plant sloppy, wet kisses to the nearest area of his skin available: his chin. No longer afraid or concerned for her resistance, he slipped his hand in further, cupping her entire sex and grinding with his palm as she made sweet, sensual noises. She was beautiful, her usually posed form draped upon him like a rag doll, her tightly bound hair now falling from its clip, giving her an almost wild look. The normally pale colour of her cheeks flushed a hot red, with her glasses slipping down her nose and she thrust against his hand. She was a delight to his senses. His free hand brushed her still-clothed breasts, and even through the thick weave of her kimono he could feel the pebbled nubs beneath. Groping gently, he decided she was wet enough, and as he slipped a single finger along her raw slit, her hands flew to his wrist at the intrusion. He paused, waiting as she adjusted. Squirming and twisting on the single digit, Nanao bit her lip as his thumb firmly pressed against the soft pearl of her clit. Pushing another finger alongside the other, he scissored them out to rub her thoroughly inside. Crying out, she thrust hard against his hand, her head tilted back on his shoulder. Jūshirō kissed up and down her neck, each time she tensed to thrust forward he curled his fingers inside her. Nanao began to tremble, her inner walls quivering as her whole body vibrated with sensation.
"Does that feel good?'" he asked craftily, nibbling the tip of her ear. "You want more?" Shifting her in his lap, Jūshirō spread her legs wider, exposing her to the snow-laden chill. Her flesh began to goose-bump in the cold as his third finger pushed inside. Rotating them in a tight formation, she let out a guttural cry, shaking violently. He could feel Nanao growing closer; her panting was infectious, and he found himself keeping pace, bending over slightly as he pressed faster, feeling her grip on him tighten.
"Come on now, Nanao-san, I know you're close." His voice drifted through her sex-dazed mind, confirming his words to be true. Arching her back, legs spread with his hand pumping furiously between her soft folds, she came hard. Clenching her legs together, she rode the waves of pleasure, cuddling close as Jūshirō laughed warmly and held her tight. Their warmth combined to fend off the cold in the garden.

"Was there something you wanted, sir?" Nanao whispered softly, her actions finally catching up with her as she blushed and looked away, unable to meet his eyes. A hand brushed the loose hair from her eyes, levelling their vision as he smiled brightly.
"Just Merry Christmas, Lieutenant."