Voldemort needs milk to survive. Nagini provides it.
Undoing a blood curse, no matter how long it had been in place, was always unpleasant and painful. Bones had to regrow and snap back into place, skin had to stretch and conform into the shape it had held years ago, hair and nails and other features had to rapidly grow and settle. Nagini would not normally submit herself to such horrible agony, nor would her master allow it, but at the moment it was necessary.
After she felt the last limb snap into place and her hair stop its rapid growth, she sat up on the bed. It was a small comfort her master had made sure she had, that she would not be writhing and thrashing around on the cold, hard floor while she transformed. And, as her generous master took care of her, she was going to take care of him.
She stood from the bed, ignoring the squeak from her master's annoying servant at her nudity and movement. She rolled her eyes; they had done this several times before so the useless creature should be used to it by now. Her master's most loyal follower, he often claimed- more like his most cowardly and pathetic one. He was very lucky her master still had use for him or else he would have been dinner long ago.
She grabbed the bottle that rested on the table beside the bed, uncapping the lid and drinking it in one large gulp. It was horrid and she preferred to drink it at once to save herself from the unpleasant taste that lingered after each sip. She had learned, too, that if taken all at once, it lasted much longer and took effect faster. That didn't make it any less disgusting, but she reminded herself that this was for her master, wiping her mouth with the back of her hand and tossing the bottle aside.
She made her way to the chair by the fireplace, the wooden floors cold beneath her bare feet. She was very glad her master had cast a heating charm on her while she slithered around the old house, else she would freeze to death.
The fire was going strong and had a faded carpet in front of it, sparing her feet from the cold and warming her slightly. Of course, she was more interested in the being sitting in the chair, wrapped in a dark cloth to shield him from the cold and from prying eyes.
"Hello, my lovely master," Nagini cooed, picking up her master. His body was so different from when he had first found her, nothing more than a monsterous baby, stillborn and cut from its dead mothers womb.
"Hello, my lovely pet," Voldemort hissed in return, his hand coming up to touch her face. It was so disproportionate to the rest of his body, but she found it charming. Unique, like her master always was.
"Is my Tommy boy hungry for some milk?" Nagini cooed, cradling Voldemort close to her chest, pressing him against her bare breast. "Milk to make my little man grow big and strong?"
"Don't call me that." Voldemort said, leaning against her cool body. "At least not in front of Wormtail."
At the mention of the man, Nagin's head snapped towards him, earning a squeak of fear as her inhuman eyes landed on him. "Leave."
Wormtail was all too happy to oblige, scurrying out of the room like the rat he was. While Nagini may have been human at the moment- a very beautiful, very dangerous human- that didn't mean she still wouldn't try to devour him. She had done it enough time for him to know that she cared not for what form they were in, only that she was the predator and he was prey.
Once she was sure the rat had left them, she sat down on the chair. It was uncomfortable, old and worn and dusty, but the warmth of the fire and her master in her arms made it bearable. She adjusted her grip on Voldemort, holding him a bit higher and more level with her chest as the potion began to take affect, making her breast swell slightly and start to ache.
Voldemort, needing no prompting anymore, latched onto her nipple and beginning to suckle. His hand came up to give her breast a squeeze and she sighed at the feeling, leaning back into the chair and relaxing. It had been uncomfortable at first, as she had never had children before, but she had come to like the warm and tingling sensation in her breast and her master's gentle suckling. She was sure, had her master been an actual baby, it would not have been as pleasant; children tended to not mind their teeth and bite too hard.
It was a few minutes later that her master pulled away, shifting in her arms. She switched his position, allowing him access to her other breast, which he latched onto just as greedily. She couldn't help but smile a little, her eyes slipping closed as her master continued to feed. It was cute how spoiled her master was, still the same little boy who thought he deserved everything the world had to offer and would take it all by force, even if he denied it.
She stirred when her master pulled away from her again, shifting in her arms to look at her sleeping face. Her breasts felt much lighter and she assumed the potion had finally worn off; it seemed to be doing that faster these days. She would have to teach the rat man to make a stronger dose- she would not have her master weaken and starve due to some rats incompetence.
"All better?" she asked softly, her hand coming up to wipe a line of milk that had escaped Voldemort's mouth. "Is your tummy nice and full?"
"I'm not an actual child, Nagini," Voldemort said to her, pulling away from her hand and laying down against her chest. "I do not need your mothering."
"Of course not, Tom," she said lightly, her hand coming up to stroke his head with her long nails. He did not fight her on this and she felt a bit bold. "Would you like me to sing you a lullaby? It always helped you sleep when you were younger."
Her master was silent for a moment, and she wondered if she had offended him— until he spoke. "Yes, Nagini. I would like that very much."
Still so spoiled, she thought fondly, lowering her hand to rub her nails down his back. She began to sing in her native tongue, a song of the heavens and the skies, and another about an island home child, soothing her master into a peaceful sleep.