(Note) That's what the japanese says.

This is Mariko, a female ninja who works under Jace's command. She's based off my friend Mariko

Mariko like most of S-Unit 00 does look like she'd be part of a secret military group. Why?

When Seth became general and was assigned his title (Sky General) he was then supposed to build his military unit. It is Renegade tradition that a new general choose every member of their personal army. However Seth through his many years with the Renegades and as the Master Thief Chaos had met numerous people that had amazing abilities and he felt they would be perfect.

So after selecting Mike, Jace, Mulan, Bruno, and Cara, he set off to locate these people and offer them a job. This is how he met Mariko. Through his years as a thief Seth met many assassins, rogues, and thieves but the one truly stood out was Marimaru Yoshimura. Marimaru was 10 when Seth met him; he called himself the “Greatest Ninja of the Era” and was pretty dang good. Well Seth forgot that it had been about 60 years since the last time he'd seen his Ninja Buddy.

When he got to where Marimaru's last known location was at he asked around for Yoshimura-Sama and when they showed him to Mariko. He was lost but she informed him that she was Marimaru’s granddaughter. He had pasted away but he’d taught her everything he knew. Seth recruited her and that began her Renegade Years.

She’s part of Jace’s unit. They handle all of the covert military operations, it has many assassins, ninja, and various other of those same types in it.