Dynasty Warriors Gundam 3

Just what it says, play 100 times. Note that you do not have to win, just play in a match until you win or lose. But you can get a lot of money, or rather G points, experience, and parts for your suits in these missions, so it'd be a waste to just suicide rush into Psycho Gundams 100 times.

I strongly recommend you play the first story mission for each of your pilots prior to going for this achievement, so that you unlock the ability to increase their friendship level. Note that you can also unlock the ability to buy licenses for your suits by using them in online missions, you just won't see a screen pop to that effect like you would in story mode.

If/when you hit the point where this achievement is feeling like a grind, stick to Forever Four and just keep taking out the Psycho Gundam over and over. You get a ton of points and experience, even if you're not the one who dealt the finishing blow. And it's still an easy fight if you set the # of players to just 2 or 3 instead of the full lobby of 4 that takes longer to fill.