u/Gakuki

We saw how, after inflicting the wound that ultimately proved fatal to A Kou, he launched an attack that ripped off his helmet and left him with one eye.

But we also saw how the wound spread beyond his eye and reached his face, and at times he looked like he was about to faint. I wondered if the wound might have caused him permanent damage in addition to the loss of his eye, and that's why he's no longer fit to be on the front lines.