The armor was activated by using the phonic gain from a Zwei Wing concert, but Ryōko Sakurai's sabotage of the safety gears caused an explosion in the laboratory which caused it to be presumed lost.
The armor reappeared two years later being worn by Chris Yukine, who had been loaned it by Finé. Its weak offensive and defensive capabilities caused her to soon discard it in favor of her Symphogear Ichaival, at which point Finé reclaimed it for herself. Based off data collected from Hibiki Tachibana, Finé was able to fuse herself with the armor, and it became her primary relic until her death.
Though labelled an armor, the Nehushtan Armor is actually very weak defensively. Its primary abilities instead lie in its infinite regenerative capabilities. While easily broken, the relic can completely heal itself within seconds of taking damage, and can regenerate from near-complete destruction. For offense, the armor is primarily equipped with a set of long chain-whips which hang off each pauldron. These whips are not exceptionally strong in battle, but can extend to virtually infinite lengths, enough to pull a fragment of the moon from its orbit. Furthermore, the whips can be used to hurl large balls of energy at an opponent — this attack is called "Nirvana Gedon". However, only Chris was seen to use this ability. The user can also utilize the whole armor in a wide-range attack called "Armor Purger", which will also cause the armor to be removed from the user's body. Again, only Chris was seen to use this. Finally, the Nehushtan Armor grants its user the ability to fly, though the exact details of its flight capabilities are unknown.
Like the Symphogear, the Nehushtan Armor changes its shape depending on its wielder. When Chris wore it, it was silver and covered most of her body save for her face and the undersides of her breasts, while Finé's version was primarily gold and exposed much more of her face and body. The anime keywords state that Finé has a higher mastery of the relic than Chris does.
Wielding the Nehushtan Armor is something of a gamble for the user, as the Nehushtan's regenerative properties cause the armor to invade and start fusing with its user via any open wounds they obtain while wearing the armor. If this process is not halted, the armor will continue fusing with the wearer until it consumes their whole body. After Chris wore the armor, Finé would make use of her regular electrocution of Chris to shock the fragments of the Nehushtan Armor inside her body into an idle state, when they could then be safely removed, putting an end to the contamination. It is unknown if there are any other ways to stop the constant fusion of the Nehushtan with its user.
Notably, it was Finé observing this fusion of the relic with Chris, along with the existence of Hibiki as the first medical case of a fusion between a relic and a human being, that led to Finé becoming interested in capturing and dissecting Hibiki and further creating a living fusion of her own. Finé would later proceed to become one with the Nehushtan Armor herself once Chris proved useless to her and Kadingir drew nearer to completion.
If fused with a user, the regenerative abilities of the armor are extended to the user as well, causing them to become nearly immortal. Only an attack on the scope of Durandal's Synchrogazer can overcome this regeneration and destroy the armor, which will cause both relic and user to turn to ash.
The Nehushtan Armor seems to be able to be turned into energy and summoned and dematerialized at the will of the user. Finé was seen to take the broken armor scattered by Chris into her possession this way, and summon it again in the need of combat. Notably, the armor is seen to be summoned to and from her hands.
In the manga, Chris is seen attempting to summon the armor after Finé takes it back, but her attempt fails, as Finé has taken command of it. Given Finé's dialogue in the same scene ("Using something you borrowed as if it actually belonged to you is very poor behavior, Chris"), it's possible that she had full control of the armor all along, and only let Chris use it for missions.
The Nehushtan (or Nehustan, Hebrew: נחושתן or נחש הנחושת), in the Hebrew Bible, was a sacred object in the form of a snake of brass upon a pole. The priestly source of the Torah says that Moses used a 'fiery serpent' to cure the Israelites from snake bites.
- According to notes from the manga, the "tights" and presumably the rest of the Nehushtan Armor are made of tightly-packed small metal scales.