I don't really care if they make Gren non-binary, as for me, the rest of the story was the real emotional hit. The story of a soldier, suffering from PTSD, feeling isolated not just because of the experiment done to him, but because of the life he had. It's why the beginning and end of that 2 parter Jupiter Jazz, is so poignant, and is frankly my favorite arc in that series.
An old man on a colony world, sitting up with a young boy, sees a shooting star. The child asks what it is, and the old man gives what is, at first, a very lame religious sounding answer. "A lost warrior, returning home, a poor soul etc etc". Then when you watch the end, and you see what it is, is Gren's starship, burning up in atmo, with his corpse. Because he felt like his life only made sense on that world where he fought. And so now it recontextualizes the old man's opening comment. He was alive during the war that took place there, so he knows the effect it had on the soldiers. And he's probably seen that very thing, for years, as soldier after soldier, unable to cope with the things they did, and had done, commit suicide "coming home" to that planet. And so he tries to phrase it in a way that doesn't upset the child, but also pays respect to the people who fought there in his past.
Given how often I've heard from soldiers who only felt like the world made sense while on deployment, and how adjusting to civilian life often ruined them, this is incredibly powerful.
I honestly forgot he had tits in the anime, as it was such a non-issue for what his real problem was in that arc.