The above guide is fantastic, I used it.
However, this is a supplement as people are worried about beating the seven level 44 giants on a first run.
This is a little trick to show you how to solo the giants with one character, Machina, and I did it at level 32.
Switch the difficulty to cadet, and equip the skill cyclone drive. Mine was fully upgraded.
Just repeat this on all seven giants for your achievement