Tasara doesn't know what the Domain was thinking, sending this girl here. Either they're more desperate than she thought, or this girl is extremely foolhardy. Likely the latter. She's, hm, maybe three years out of training, judging by her stamina. Not much finesse, but exuberance in abundance, and a stubborn refusal to admit she's outmatched. If they were further from the city Tasara would flatten her, but the goal is defense, not destruction.
Into the box then it is.
Said box turns out to be an elevator, which moves silently and smoothly downwards at some gesture from Itachi. She and Shisui are in fact confronted when it opens, something about codes not getting passed - Itachi convinces the person codes were passed, then, after the person fades back into their waiting place, meets the two magical girls' eyes and nods along the hallway. 'Slow,' she mouths.
A few more guards are tricked or subtly disabled - of varying apparent age, the youngest they see is probably around eight, and the oldest sounds maybe in his twenties - until one glances past Itachi, lands her eyes on the magical girls, opens her mouth -
And she falls, dead, Itachi's hand resting lightly over her chest.
"The alarm will be raised, soon," Itachi says softly. "We should move quickly. Our first destination is nearby."
They get to a heavily sealed door. Itachi says, "I can get through this, but I need Shisui's help, and I'll need to concentrate. There might be people coming this way. Try to disable rather than kill, I can alter their memories of your presence, but killing is an acceptable alternative. None should be any sort of threat, this isn't a well-guarded base."
The two shinobi get to work.
The first person to come across them is a white haired boy - maybe nine or ten - in a blank mask. He seems to mostly be spying, or perhaps waiting, and doesn't try to attack.
This is still enemy territory. She doesn't actually hesitate. A Disable erupts from her hands to seek his head, to blind, deafen, and stun. She materializes her sword behind him and pulls it toward her, pommel first, to knock him out.
He goes down, hard.
Further hostiles are more cautious about revealing themselves, but once there's enough they grow bolder, striking rapidly towards the group, some hiding their tracks well enough it's difficult to sense them approaching.
It's hard to stealth through area effect attacks. Quiet ones, but it's not hard to fill the hallway.
And unfortunately for their attackers this hallway was designed to be easier to defend from the magical girls' current position than to invade.
Itachi gets through, shortly after the base apparently runs out of incautious operatives.
"Got it," she says, opening the door into an office. "Shisui, help me grab and seal files."
They make quick work of the office - Itachi leans towards 'grabbing everything' - and then of other archival rooms; there isn't much more opposition. Itachi goes over the downed enemies, tapping their foreheads, and says, "I sealed the entrance behind us, so none of them should have been able to escape, but that's still a small possibility. Still, they wouldn't have descriptions of you two, at least."
Nod. "We'll want to go over what's here, sort out what we should pass on, figure out if we need to hit other bases - but this was the central base; Danzo kept fewer forces, more information. There's bases with trainees, which might have information on Danzo's actions against the clans, but I suspect the Hokage will want to handle those directly."
"Indeed."
Their exit goes without note. Itachi double checks on the two unconscious guards outside - still out cold - and tweaks the illusion over them.
"The same hideout as earlier works. My family knows not to expect me back for a few days."
"That will be best. We can go faster, now that I've adjusted to you both."
Sneak sneak sneak, quietly through the forest. (They do in fact pick up speed a good bit; not nearly to shinobi limits, but they're going much too fast for someone not enhanced to ever have a hope of keeping up).
At the hideaway, Shisui and Itachi break a few seals on the files themselves, then start sorting through papers. "Does your translation cover written words?" Itachi asks, off-hand. (She doesn't intend to let them help, but it's important information to know.)