Carl's laundry-hamper-looking equippable backpack — the trick that lets Katia carry over a ton of hidden armor-mass.
The Ugly Ass Backpack is Carl's crafted breakthrough for Katia-Grim: a big, open-topped metal basket with reinforced dingo-hide straps, made equippable on his new armorer's table. Its genius is an inventory quirk — items placed inside a container that's then stored in inventory count as the pack's 'contents,' so when Katia equips the backpack (loaded with ~1.25 tons of dense dwarf-robot metal and reed-like poles), all that mass becomes part of her body. Equipping it turns her into a multi-ton super-tank; unequipping (mentally pulling it into inventory) shrinks her back.
The straps are cosmetic — they'd never hold the weight — existing only so the system calls it a 'Backpack.' Cumbersome and slow to don (~30 seconds via a stand-and-slug-form ritual), it nonetheless unlocks Katia's true class potential, and Carl already schemes to make it bigger and denser.
A large, open-topped metal basket 'like an oversized laundry hamper or giant quiver' with reinforced dingo-hide shoulder and waist straps; loaded with protruding metal poles.
The load-bearing exploit that makes Katia a variable-mass super-tank.