Heart of a Machine

Chapter 1

When Aloy awoke from the procedure, she could tell something was different about her. Her movements weren't hindered when she got off the pedestal she was on, but she could tell. She was on a pedestal in the core room, similar to the one Fa was on when she was being altered by the corrupted version of HEPHAESTUS. "Ah, you are awake. That is very good. How do you feel, Aloy?"
Aloy rolls her shoulders, stretching out muscles that are no longer there, more so out of habit than anything else. "Different. I don't feel any stronger or anything like that. Just different."
"That is to be expected. Would you care to test your current capabilities?"

Aloy stands before a massive humanoid armored machine with a giant minigun for a hand. "Attempt to enable your helmet via mental command."
"Ok." Aloy knows that the helmet is there, and tries to think if it just kind of appearing on her head. And it does. The segments of the helmet unfold from inside her head somehow and wrap around her head in its protective embrace. "Woah."

HEPHAESTUS gives her a rundown. "While the base functions of a Focus are available without the helmet, it gives you more advanced options. I've upgraded its scanning capabilities, so it will be able to register new data almost instantly, and over a wider range. Scan the machine before you."

Aloy looks at the machine that is in the room with her, and HEPHAESTUS was right. Almost instant information. It was called a Juggernaut. "Speaking of the big guy, I thought you were making machines to help people?" Can't blame her for being paranoid.
"Having seen your past experiences, both with trusting others and AI specifically, I cannot blame you for your suspicion. It is indeed made to help people. This design specifically is made to defend against machines made by my corrupt predecessor. But for now, its purpose is to assist you in testing your combat functionality. I have taken the liberty of providing you with new weaponry."

Another humanoid machine, this one much more proportionate to a normal person, albeit a bit smaller, comes into the room and places a supply cache at Aloy's feet. Scanning it reveals the name Assistant. Opening the cache, Aloy finds a folded bow made of the same white metal as machines, and a tube of the same material. "Alright. I appreciate the effort, but how is a bow without a string and a random tube going to help me?"
"There is a button on the side of that "random tube". Press it."

Aloy finds the button on the side and presses it, and the tube unfolds into an impressive spear. "The spear is capable of being compartmentalized for lightweight travel, and has a hard light blade, and as such, cannot dull like traditional edged weapons."
Aloy inspects the glowing blue blade. "How good can it cut?"
"Why don't you find out?"
An Assistant stands before Aloy. "Uh, are you sure? I've never attacked a machine that wouldn't fight back before."
HEPHAESTUS assures her. "It is the only way to test the weapon before going into the field."
Aloy shrugs. "If you say so." She goes for a light attack, thinking she might do some damage to such a small machine, but she is surprised when the whole arm comes off, the place where it had been cut glowing with heat.

Aloy appeases the machine spear. "Not bad. I'm guessing the bow has a surprise for me too?" She grabs it and finds the button she supposes activates it, and it unfolds, revealing a hard light bowstring. "Of course it does. You're full of surprises HEPHAESTUS." An Assistant provides a quiver that matches the aesthetics of the rest of Aloy's ensemble, with different types of arrows sorted into each section, also matching the aesthetic. It leaves with the damaged Assitant, taking its arm with it.
A series of Assistants line up in front of Aloy. "Feel free to practice your aim."

Aloy didn't know if it was the newfound strength in her arms, the quality of the bow or the intensity of the more advanced arrows, but every shot his twice as hard as it did before, which is perfect for what she needs to do. At HEPHAESTUS' order, she takes a few strands of "hair" in her hands and inspects it, noticing an odd sheen to her iconic fiery locks. "Your hair has been replaced with fibrous solar cells that collect solar energy from being exposed to the sun. They are currently running at 50% capacity."
Aloy looks around the room in a facsimile of eye contact with the AI. "Why only 50%?"
"I brought into account humans preference for style and gave you the option to keep it close to your original colour, or use a mental command to invert them in order to run at 100% capacity at the cost of a colour change."
Aloy thinks about her hair working better, and it shimmers in her hand, going from her usual red to a dark blue colour. "No reason to do things half assed. Besides, it's not too bad."
"As you wish. Let's move on to your physical abilities."

A carrier drops a crate of resources in front of Aloy. "This cargo weighs approximately 635 kg, the world record for weight lifting on the Old World."
Aloy inspects the crate. "The Old Ones were intense." She grabs the anchors the carrier used to grab and carry the crate and lifts it above her head. It was definitely heavy, and there was definitely strain on Aloy's new body, but the fact she could lift it at all amazed her. She drops the crate. "That Juggernaut has been in here the whole time. Let me guess, testing my shield?"
"Correct. If you are worried about receiving bodily harm. Pain in your cybernetics has been dulled and replaced with an HUD warning, and I will be prepared to administer repairs immediately. To activate your shield, press your fingers together and concentrate."

Aloy presses her fingers together, like she's about to give a high five and thinks about the shield, and it appears in front of her palm, much less flickery and damaged than the one she carried with her. "Ok, that's handy."
"Correct. As well as operating as a protective barrier, you can also use it to glide as you did before, with much more efficiency. Care to examine its integrity?" The Juggernaut march in front of her and prepares its minigun.
"Bring it." The minigun charges up and starts letting loose a barrage of energy blasts that hit the shield. The impact pushes Aloy back a little, but the shield doesn't waver.

When the minigun stops, the shield is still up, not even flickering after that abuse. Already getting the gist of how all these things work, she lowers the shield and extends her right arm, her hand holding away to reveal the plasma canon, and she fires it, the impact knocking away a few sizeable chunks of armour plating from the Juggernaut. Aloy looks at her hand as it folds back into shape, flexing her fingers. "Impressive. But one last thing." She retracts the helmet back into her skull. "That kinetic energy thing you mentioned, how does it work?"
A hologram of Aloy as she is now appears before her. "Each of your joints has motors that are triggered by your movements." There's a brief close up of her elbow, an x-ray revealing said motor. "When they move, they will generate electricity." The hologram moves its elbow and triggers the digital motor.
"That'll be useful. I should go find AETHER. Uh, thank you for his by the way."

She goes to leave, but is stopped by HEPHAESTUS. "Before you leave, there is another feature you should be made aware of." Another close up of a holographic helmet. "During the procedure, I scanned the Master Override on your spear, and used it when designing your new one. However, I keyed the Master Override to your Focus, allowing you full control over machines indefinitely."
Aloy is... flabbergasted, to say the least. "Ok. Telling a machine to fight is one thing, but you're saying I can CONTROL control machines now?"
"That is correct."
Aloy stares at her mechanical hands, stunned by the power she now has. "You turned me into a killing machine."
HEPHAESTUS asks. "Is that not optimal?"
Aloy shakes her head. "No, it's fine, just... surprising." She shakes away the inhibitions she has and fixes her new spear and now on her back. "I might come back some time HEPHAESTUS. But right now, I have to go find AETHER." She dons her helmet with a dramatic clang.

(The Juggernauts basically look like space marines from 40K, but with a Horizon machine aesthetic. And the Assistants are essentially Cogsworth from The Last Knight, but in the same aesthetic)