A very old fill from the now-dead Megaten Kink Meme. I don't have the original prompt saved.
His hands trembled slightly as he tucked the blackened bolt that had once been part of Aigis' body in the breast pocket of his shirt. It was not large or heavy, but its weight still pulled at him, seemed much greater than the simple tug of gravity.
The trembling did not quiet as he leaned in and began to untie the big ribbon around her neck.
Her words still echoed in his head - The thing that's most precious to me is to be at your side. And though he couldn't say why, he had a feeling that he may not be able to grant that wish for much longer.
The knot on her ribbon was stubborn and did not come untied easily. His fingers weren't quite as strong as hers.
He felt somewhat awkward doing this. Even though Aigis was technically 'naked' most of the time, and he had grown used to it, it didn't feel anywhere near as natural to actually undress her. He wasn't sure what would happen when he finished, either. It wouldn't be like making love to a human girl - even as human as Aigis has become - but he wasn't sure that was the comparison he ought to make. This was a unique experience, probably something no one else would ever be allowed to feel, and it was more akin to touching her heart. Except this time, it would be in a very literal sense.
No wonder his hands were trembling.
The ribbon finally yielded to his efforts and came off, and he draped it across her lap before going to work on the buttons on her uniform. Those were a lot easier to deal with, and the jacket and shirt soon hung open, revealing the pure white of Aigis' chest and stomach. Her 'skin' was hard, but with a slight texture, much like fabric over metal. It didn't quite feel like any cloth he had ever encountered, but then again, Aigis herself wasn't like anyone he had ever encountered either.
There was a small hatch at the base of her neck, just a little smaller than the palm of his hand. Its outline fit so well into the texture around it that he'd have missed it completely if he hadn't known he was looking for something in that specific area.
As he carefully touched a finger to the rectangle, it yielded, slid in and down, out of sight. He jerked his hand back as a metallic grey base slid out in its stead, presenting what had to be the thing Aigis had been talking about, what she had named the 'Papillon Heart'. It was red, a perfect gem-like sphere, and seemed lit from within by a faint glow. At first glance, it did not look like a mechanical thing at all, until he leaned closer and noticed the texture of fine circuitry covering it, just barely visible.
He reached for it, but hesitated, and stopped just before making contact. Would this hurt? His hands were rough and callused after the past year's battles. The indelible, irrevocable proof she wished for - what damage would it cause?
It was too late to back out. He bent and, holding his breath, lightly pressed his lips against the red sphere. It trembled like a living thing, not the steady ticking of a machine, and Aigis whimpered like a wounded animal at the touch.
"Does it hurt?" he asked, careful not to breathe on the delicate circuitry.
"No," she said, in a small, breathless tone. "But could you... just one more time...?"
Feeling rather more confident, he kissed her again, a little more firmly. This time, the noise Aigis made seemed more content than hurt.
No matter what tomorrow may bring, he could at least stay with her tonight. Maybe that would be enough.
It would have to be enough.