According to a Famitsu interview (nabbed by DualShockers), Motomu Toriyama "wanted it bigger" with regards to Lightning's chest, a fact he found funny when interviewed on the subject. Lighting -- who Square Enix wants us to believe is a strong female character -- gets her jiggle on with various costumes in Lightning Returns, her model designer showing off how much you can make her chest bounce.
"Yes, her chest jiggles," explained Nobuhiro Goto. "Since everyone can decide what costume she’ll wear, you can make sure it does (laughs). By the way, since Lightning swings her arm when you change her weapon in the menu screen, that’s a recommended action for sure-fire jiggling! To see it even better it could be useful to equip a small shield. Look forward to it!"