This is fan service at its best. Square Enix have added some Final Fantasy XIV costumes in Lightning Returns: Final Fantasy XIII, and the lead protagonist Lightning will be able to wear them.
However, considering her serious nature and role as protector of the world, there seems to be a disconnect and the costume doesn’t really suit her. There’s also a victory pose with sound effects which she does which can be termed as seductive.
The costume is from the Miqo’te race from Final Fantasy XIV: A Realm Reborn. The game is the last one in the Final Fantasy XIII saga and ends Lightning’s journey and it looks like Square Enix wants to end the saga with fans wanting more of Lightning.
She can also wear a Cloud costume from Final Fantasy VII and a Yuna one from Final Fantasy X.
Check out the image below.