A mecha game that's... premecha. When mecha were very first starting to hit the battlefields, and everything was very much a prototype.
You're a ground troop, part of a higher-level clandestine group. The story happens in "flashbacks", where you're telling your story to a therapist (It later turns out that some aspects of the story were false as you told them, and you're in a secret military "loony bin" of sorts). The first missions are hands-on spy missions, where you use your various tools to see what's going on and how far your enemy has made it into mecha research. It turns out they're as far as you are, and destroying their prototype goes south...
The fourth mission, post forced-failure third "destroy prototype", takes place in a prisoner-of-war camp. Your goal is to escape, but you take note of things that will later be very important- strange medical devices, a strange amount of bodies without brains, and many other details that were actually "added" (psycho, remember), on your way out. You'll have a chance to fight or slip out undetected nearer the end, but getting caught before you're armed is a death sentence. This is not on rails, and you are allowed to attack without a weapon- a lone guard with a pistol might be a good target.
The next few missions are you trying to get out of a very hostile place. This is also the first turning point in the story, where your choice affects the rest of the story.
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In the end, all the "changed" things are revealed as to what they really were- the camp didn't have half of what you described, but rather, you add details from a later mission where you learn what the enemy are doing, and the ethical issues- they're taking POWs, injured soldiers, and anyone with combat experience, taking and "reprogramming" their brains, and putting them in the mecha as "drones", bypassing the difficult-to-control mechs that few can pilot with any skill at all.