FANSERVICE! YAY!... ALSO SPOILERS!
Ok easy one. Once you beat Viola's AI once and for all you will have to escort Ken's Ardjet.
First take out the first few Raptors. Then grab hold of her and head down to the lava. Do NOT touch the lava or allow Ken to fall in.
Just spend a good 15 seconds or so floating a few feet (or few dozen meters considering the size of Jehuty) above the lava until Ken complains once or twice.
Then complete the level as normal. You know you got the achievement when a hot girl without her flightsuit sits next to you in your cockpit.