The appearance of a Corpse outside of the Lightless Realm has caused panic amongst those whose job it is to protect humanity, leading to their demanding that the Argent be deployed within said realm forthwith to prevent any further such incidents.
Quite reasonably, those in direct charge of the project point out that this would be extremely dangerous, and thus insist upon waiting until they find a suitable pilot for a second prototype "Reaper". The director of the project seems keen to test Heito in the cockpit, but he remains elusive after Emiru's death, leading to Raika hopping into the cockpit first, only to last less than a minute under the intense mental strains caused by this machine.
It seems that nothing is taboo when it comes to finding the right pilot for this unit, and thus a scheme is concocted to bring Heito and Akashi together, letting the sparks fly between them, in direct contrast to the odd relationship between Akashi and Sasame, and in turn her own relation to Minashi, which seems to suggest links in the past between those in Gargouille. Once Heito's hatred boils over, his anger soon turns into an attempt to do bodily harm to Akashi... how fortuitous that someone has left this new protoype mech in his vicinity, only to find that he has the ability to pilot the machine with ease while also giving us some clues as to the origins of these monstrous devices.
For everything that M3 the dark metal gets right (which isn't all that much, admittedly), it gets a whole lot more wrong. Its over-the-top "bad guys" are still incredibly irritating rather than the dark faces of humanity that they purport to be, and while I'm grateful that the series is piecing together its elements in ways that are obvious to the viewer without being overly forced down our throat at this point that doesn't really do enough to make the actual narrative compelling beyond some vague feelings of "ooh, it's trying to be a bit like Evangelion" - something that you could be said about so many shows it doesn't exactly make it unique either.