This was a novel I read back in the 90s. The book was in English. The time is set in the future. The US (I think? Or an allegorical nation that mirrors the US) is fighting a war against (allegorical) Russia/China, and invents a mech suit (giant robot, Gundam-style) that needs a human host to interface with it.
Military/civilian adults are recruited and only certain adults are selected due to needing a specific genetic makeup to be compatible with the augmentation process for the mech suit's harness interface.
The protagonist is one of these chosen adults. The harness, as a side-effect, requires that the volunteer willingly give up their outermost consciousness (memories, too, I think), which is fed into a feedback loop-type of chip in the augmentations, thus avoiding going into insanity when interfaced with the mech suit.
I cannot recall the name of this book for the life of me! It's not the Pacific Rim series, and I don't think it was Gundam at all. These are adults who volunteer, not forced child soldiers like in Mobile Suit Gundam. It's not the Halo series either, as obviously this is a giant mech suit, not human-sized armor. It MIGHT be a Gundam series, but I don't recall one that was themed like this.
I recall a chapter/scene where the protagonist was having flashbacks of random memories he was trying to make sense of, but of course didn't know the people in the memories because of the inhibitor in the augmentations.