So this was easily the toughest mission in the game. But it wasn't really hard. It was the only challenge mission where i actually died. Took me just under 30 minutes, died about 4 or 5 times, learned a good lesson each time. I personally think Knight Gundam is garbage for this mission. Did it in a maxed out Unicorn. His lvl 3 sp nearly fully kills any of the officers, then your in destroy mode and it's impossible to be hit between attacks if you using a lvl 50 character because of his sheer speed. I used Ace Killer, Sky Eye, and Serene Mind. Also Duo is amazing as a partner for this mission.
I was actually a little disappointed with how hard people were saying this was with the level of ease i had. I killed 27 enemy aces during the mission as well.
The key was to just defend off the first wave then go take the missile base, defend the re-spawned wave, then take the engineering bay or whatever it is called to stop the battle gauge from just re genning. Took me a couple of waves of ace's to notice that lol. Then just let the Ace wave's come to kill the gauge and let the missile base take your zones. It was easiest when they group attacked me. I was getting either 4 or 5 aces at a time, just wait with a full musou use Sky Eye to let them all pack up on you, full musou with into a wall and kill 1-3 then just hit the remainder who back flip and dash into the wall once or twice for the kill. When I finally entered the enemy HQ the only zone it had left was the fortress right outside it's front door.
At the end when you get jumped, just key on the two Musha's and ignore the Knight. Use the same strategy from before and they will die relatively easy. Then just manage out your musou to always have some and poof easy. Only got hit once in the battle with the final 3 in my first try.