The upcoming issue of Jump provides details on two of the more mysterious areas of Final Fantasy XIII-2, the Caius character and the Fragment system.
Regarding Caius, fully Caius Ballad, the magazine reveals that he is in pursuit of Noel. He has tremendous strength. However, he is cold and does not show his feelings, so no one can tell what his goals or thoughts are.
As previously detailed, Fragment is the name for the quests you clear in the game's various time periods. What's actually going on is, you're clearing up time paradoxes in each era. when you clear a paradox, you receive a fragment as your reward. The fragments are inscribed with bits of knowledge and folklore/legends.
[via FF Reunion]