The hard ending ending is easier (though still very hard) if you get the upgraded Polar Star and the Nemesis- the first one ignores the leveling system altogether and the latter has it reversed, so the "weapons drop to zero" thing isn't nearly so bad. Getting the Nemesis involves a time-consuming but fairly easy sidequest, but the spur requires both the booster 2.0 and that you wait until after the labyrinth to upgrade your starting gun, which makes the fights with both Monster X and the Core much more difficult.