This is an ARC (Anti-Robotics and Computer) trooper on the Astral Queen. She is wielding a Thunderbird, a firearm that uses plasma instead of typical slugs to immobilize any equipment that uses electricity and can burn flesh too.
She was heavily inspired by Rivet from Ratchet and Clank and her face mask is from Nausicaä of the Valley of the Wind. This is also probably an extremely dangerous position to hold the gun in.