So, long story short, the MC asked for retirement, and the military simply pretends to give it to him, and puts him in a path that, no matter what, he ends up fighting for them. He still has to answer their calls, the endgame of the academy is recruitment for the military, they force him to interact with students so that he gets attached to people and make him believe that he is choosing to protect them by his own will and if he refuses to interact with them he is inmediately recalled to active duty.
Also, it speaks volumes to the lack of proper upbringing that MC doesn't have inmense political clout. Apparently, the can't even maintain proper national security without him yet he lets himself get pushed around. That alone tells me that they left him uneducated and ignorant of the real world on purpose so that he can be more easily manipulated. They are practically treating him like a slave, except that his chains are barely visible and his cage is really shiny and distracting.
These people are really fucking twisted. The story would be 100 times more interesting if the MC saw through this bullshit and tried to take an alternative path, but it won't happen because muh fantasy high-school story.