Nathan woke up in the middle of the night, with that horrible malaise.
The feeling of wanting to vomit, but knowing that wasn't what was
going to happen. It was time, he'd held it in check too long.  His
skin was sweaty, clammy, and glowing slightly green.  When he'd asked
Aarth's doctors how long he'd have to remain like this, to be cured,
they said a year, maybe two, and they'd check again afterwards.  He
honestly didn't think they had the slightest clue about whether he'd
ever be able to be rid of this curse... but thoughts for later.  For
now...

He didn't regret saving those miners from the radioactive cave.  It
was what he swore to do when he signed up with Athene, but this...this
was never a planned outcome.  He turned on the light and took off his
clothing, looking across his naked body as he sat down in a chair.  

It started first, as it always did, with circuit traces starting at
his toes and starting to run up.  The skin rippled a bit, circuit
lines appearing underneath, roughly where some of his nerves would've
been, and then the skin shimmered, hardening and taking on the
appearance of steel.  His toes merged, the whole appendage of his
foot becoming simply akin to an articulatable boot.  This happened at
both feet at the same time, and for now, they weren't responsive.  He
shivered a bit at the chill they brought to the rest of his body, as
blood pumped down there and came back a mixture of lubricants and
hydraulic fluids.  Sliding up to his knees, the skin continued to
take on a metallic sheen, mostly in the color of metallic denim blue
jeans.  He'd never figured that part out, but at least he wasn't
running around naked as a flesh colored robot.

His knees...that was always an unpleasant part.  The bones popped,
crackling as they shifted over to articulating servos.  Nathan drew
in his breath sharply, trying not to scream as it continued up, his
thighs becoming so much steel and servos and pistons.  As it reached
his groin, he could feel plates form over where his nether regions
would be.  They didn't open, or so he thought; truthfully, he'd never
tried.

Not paying attention to that, it slid up his chest.  His scar from
saving Dawn took on an even more metallic feather sheen as it was
replaced, and his internal organs started to rearrange.  Here, he DID
feel like he was going to vomit, and he was unable to stop himself at
least twice as his entire digestive system turned into a power
distribution plant, and loads upon loads of batteries.  His heart
fluttered...this was one of the worst parts, then seized entirely, and
the familiar heartbeat in his ears dimmed, quickly replaced by a
slight 'whirring' sound as the hydraulic pressure pump replacing it
took over.  

His arms were starting to cover over with metal. The definition of his
muscles stayed, maybe because of his vanity, and his mark to Athene
stayed as well. His hands covered over with steel, becoming powerful
hydraulic grippers. No flesh over them, but much stronger than any
human's grip.

Next...the head. This WAS the worst part.  He stopped breathing; he'd
still been doing so instinctually, and momentarily panicked about
it.  Once that was done, it was up to his chin.  The scars from the
bear attack long ago appeared as marks and dents on his plating's
coloration,, and his vision flickered out briefly as cameras took
over.  He gritted steel teeth as auditory microphones took over his
ears, his hair solidified, and suddenly, then it was the absolute
worst part.  He lost consciousness with a splitting headache.

How long passed wasn't more than a few moments, but when he woke up,
he could see again.  Data was overlaid on his vision, showing ambient
conditions, charge level, any particular damage to his frame or
systems.  "Unit NRenfrew operational, systems nominal." displayed
briefly, and he stood up, listening to the whirring motors as he did,
and turned around to see what was different.  Aside from him, it was
all the same.  He looked out to the moon and saw a chart of its path
across the sky, the current time, and approximate moonset, sunrise,
and full moon date filtered into his mind.  And now...the big
question.  He went to the bathroom and got a lock of his hair he'd
cut off a few days ago.  They'd told him there were better exemplars,
but he used hair, because it was less gross.  He ran his hand over
it, and was rewarded with a standard Geiger counter clicking sound. 
Rapid, but his subsystems read the data coming in and reported it back
quickly.

"Biological contamination at 23% above lethal dose.  Down 5% from
last month.  No pattern established with prior samples.