The Armor Purge (アーマーパージ Āmāpāji?) is an ability that the user use to forcibly release her currently-wielded Relic from her body by making it " explode ", shooting everythings arround her with the fragments in a small area, leaving the user in a temporary powerless state.
The first use was in Episode 7 by Chris, after taking a powerfull blow from Hibiki which greatly damaged the Nehushtan Armor, the armor, to repair itself was using Chris' energy, futher harming her in the process.
She decide to discard it by using the Armor Purge, before using Ichaival to fight Hibiki.
The second time was during the episode 12 of G season, when Chris was surrounded by Noise and was not able to use her Armed Gear to fight because of the Anti-LiNKER gas used by the Dr. Ver.
She use it, hoping to destroy all the Noise, unsuccessfully, she is saved by Tsubasa, who was able to transform using a personal method.
The third use was by Hibiki in the last episode of AXZ season, after being caught by Adam Weishaupt, Hibiki use it on Chris' advice, freeing herself from him.
We can also note that Hibiki didn't end up naked after using it.