warning

this character's backstory contains spoilers related to the Sorrow of Werlyt raid series.

childhood

To say he was born with a silver spoon in his mouth would be an understatement.

His father, Emilius cen Iulia, was a well-known artisan working directly under the emperor; once a simple tailor, his striking designs had attracted the emperor's eye, and eventually landed him work as lead designer for both the royal family's garments and the Garlean army's uniforms. Now renowned for his rich purple dyes, a closely-guarded secret that no one seemed to be able to replicate, he had done all of the hard work of climbing up the ranks and building himself a comfortable life in Garlemald - and all Cato had to do was reap what his father had sowed.

For the first few years of his life, he had it all going for him. Safe in the knowledge that he'd one day inherit his father's business, had access to the finest education Garlemald had to offer, and that he was safe from the army's grasp, he lived indolently in the upper crust of Garlean society, with little to worry about.

Until - a knock at their door.

the weapon

one of cato's cousins was taken for an offshoot of the weapons program, and didn't survive being merged with their machine. cato's the closest genetic match they can find
so they're planning on relinquishing him to continue the experiment
cato's father turns to his fortune and some of his contacts to find someone who's willing to help: Seneca.
Seneca, without warning authorities, takes cato under his wing and makes him part of his own program - a series of experiments to imbue garlean soldiers with the same ability to manipulate aether that eorzeans have
(cato is his SECOND try at the experiment, seneca was his own first subject, but no one knows that except maybe aika?)

the escape

seneca's experiments start and cato becomes "unusable" for the weapons experiment. seneca gets away with it by pretending that he didn't know about those (which would be true, it'd be above his clearance level?) and cato's dad gets away with it by saying "well i couldn't very well say no to a Mal, could i?"
so for years cato gets experimented on. doesn't interfere with his life that much except he needs regular care which his dad passes off as "checkups" because hes rich and deserves the best healthcare obviously ^_^
so as far as cato knows he has had a mysterious illness since childhood but it's totally under control don't even worry about it
this continues for years

modern day

cato's dad eventually catches wind of some unrest in garlemald (the different . whats the fucking word. the different parts of the army.)
sends his son out """ON VACATION""" to eorzea extremely tearfully with a bodyguard (amandus)
cato isn't happy but won't say no to his dad and to expanding his horizons
(garlemald then explodes but shhh shhh he doesnt need to know)