Throughout the manga, it's hinted that, despite seemingly being a mindless robot, The Moon possesses some form of empathy towards humans. This is most obvious when it cries when its operators are in distress— the kids dismiss it as leaking oil, but seeing as it only happens when they're going through emotional trauma, it's reasonable to assume that The Moon is experiencing emotions too. Also, while The Moon is supposedly only able to move when the kids command it to, it doesn't do that in the first arc. When the kids accidentally crash it into some power lines, The Moon seemingly takes over, catching a hydrogen bomb and carrying it out to sea without any direction from them.
This also casts the ending to the manga in a new light. We're led to see it as a Downer Ending, with the kids all dead, The Moon no longer able to move, and the Earth doomed. But if The Moon really is sentient and able to move by itself in extreme situations, that might not be the case. The kids' deaths might actually be a Heroic Sacrifice, allowing The Moon to destroy the mold-making machine and save the Earth.
