Disclaimer: Most likely a lot of things here are probably way out of place in the timeline, but try as I might, I couldn't figure out when things actually happened in the FMA world. This is about 50 - 100 years ago...
----------The Caduceus, Part 1----------
Dante smiled confidently and set her palms down on the tile floor, on the outer ring of the human transmutation circle. There she held them as the golden light rose out of the lines and spun into the air, creating a whirlwind of light.
Dante was always awestruck by the beautiful vortex of light dancing around her. She had only performed human transmutation twice before, but still it was a sight to see. She expected no lesser display by the man known as Hohenheim of Light, who designed the circle.
She was not alone in the room; five others accompanied her. Three homunculus stood along the left wall, watching in astonishment. There was a tall man with spiky, dark green hair and tight black clothes; he was called Envy, and was the first homunculus created. Next to him, a much shorter one stood; a chunky and bulgy homunculus suitably deemed as Gluttony. The final homunculus present was a tall and striking female; she had a long slender body and dark red hair, and her face was smooth and supple. This, of course, was Lust.
A fifth person, a human, stood on the opposite side of the circle. He had blond hair and deep eyes, and he clutched a small red stone tightly. And behind him, a young woman--about the same age as Dante--was tied to a chair and gagged. She was unconscious.
Dante watched with wide eyes as electricity and smoke jumped around in the center of the circle, and she couldn’t see what it contained. Then she felt it coming. She sucked in her breath as the center of the transmutation began to brighten drastically, and the world itself seemed to fall away at that point.
Then all went stark white around her. All she could see within the light rushing past her was the outline of doors swinging outward towards her. The Gate opened wide and extended its dark, tendril-like arms toward her. Instinctively, she tried to pull away, but she couldn’t move. The black threads wove around her body.
What were they going to take this time?
She watched with fear as they roved her body in search of payment, and her teeth were gritting together. And one of the long arms found her chest. She screamed in excruciating pain as it felt like something dug into her chest and through the ribcage. She had never known such pain before! But she didn’t have to suffer the pain for long; she gasped as the pain suddenly faded, and her vision went dark...
Dante slowly opened her eyes and looked up. Hohenheim knelt before her, his eyes boring into hers. She tried to stand up, but found that she was on a chair, and her hands were bound behind it.
Dante sighed. “Let me up, Hohenheim,” she said, and he nodded and moved to the back of the chair. She heard him clap, and the ropes around her wrists burst apart. Dante stood up and stretched, and looked down to observer her body. It was a bit skinnier than she expected; it would take some getting used to.
When she looked up, she saw... herself. Dante’s former body lay on the edge of the transmutation circle, the center of which was still wreathed in smoke. She shuddered as she looked into her own pallid face, and she noticed blood dripping out of the body’s mouth.
“What did it take this time?” Dante dared to ask.
“Your heart,” said Hohenheim without flinching.
Dante looked down at her new body again. “Then I was right in bringing the woman here as a precaution. I suppose you can never be too careful... as far as human transmutation goes.”
Hohenheim nodded, then held up the red stone in his hand. It was now only half the size of his palm. “A considerable amount of the Stone has been used up. It should only be enough for a few more jumps.”
Dante smirked. “Then we shall have to find a new one soon.”
Hohenheim nodded, but Dante took note that he seemed to frown a little at that statement. She stared at him for a moment, but he just stared forward into the cloud of smoke, unflinching still.
Finally, Hohenheim looked over at her and grinned slightly. “That green hair is quite becoming of you.”
Dante’s face turned beet red, and she looked away bashfully. After she had turned away, his smile instantly faded.
A cough from the midst of the cloud of smoke caught both of their attention. The smoke was finally clearing, and they saw that a small form inside the circle moved around on the ground.
Even the three homunculi along the wall leaned forward expectantly. Finally the smoke cleared and there was a long silence.
Envy laughed out loud. “What is this? You call this a capable homunculus? It’s just a child!”
Indeed it was; a small, naked child was curled up on the ground, his eyes tightly closed. He seemed utterly harmless, and he coughed again as the last of the smoke cleared.
“He’s not just a child,” said Dante, walking across the floor and kneeling beside the boy. “He’s my finest creation. A homunculus that will be able to age just as normal humans do.”
Envy narrowed his eyes, seeming unconvinced, and Lust smiled alluringly.
Dante scanned the boy’s body, but soon was frowning. She couldn’t find an Ouroboros tattoo anywhere on his body...
The boy looked up at her and opened his eyes, and she gasped. His left eye had no pupil; it was instead adorned with the tattoo she had searched for. As the boy looked up at her, she smiled, knowing this would be a useful creation indeed.
But what would she name him? She looked up at the three homunculi, Envy, Gluttony, and Lust. Three deadly sins. They were the Ultimate Changer, the Ultimate Mouth, and the Ultimate Flame.
Dante looked back down at the young homunculus. “You will be called the Ultimate Eye. And since you are my finest creation--”
Hohenheim read her mind. “Pride.”