Here is the full list of all 31 Final Fantasy XIII-2 achievements. It takes around 50-60 hours to unlock all of the achievements on Windows.
Defeated an army's worth of enemies.
Left behind a normal life, and began a journey through time.
Accepted a new fate in a world where everything has changed.
Visited the place where clues to the future lie waiting to be discovered.
Visited the place where the saviors of the past dream in crystal.
Acknowledged the threat facing the world, and decided to fight back.
Prepared to face a test of your determination in the rift where hidden truths slumber.
Turned your back on empty dreams and joined the battle to save mankind.
Obtained five Cinematic Bonus rewards.
Witnessed every possible Paradox Ending.
Followed the story to its conclusion.
Went the distance on chocobo-back.
Amassed a fortune in casino coins.
Spent a fortune at shops.
Responded swiftly to the appearance of enemies.
Completed an entire fragment category.
Completed every fragment category.
Defeated a powerful enemy with graceful poise.
Defeated a powerful enemy with valiant skill.
Defeated a powerful enemy with perfect execution.
Staggered a significant number of enemies.
Performed a significant number of preemptive strikes.
Successfully used Feral Link abilities a significant number of times.
Fought a significant number of battles without using the "Retry" option.
Performed a multitude of paradigm shifts.
Fully developed all abilities.
Defeated every worthy opponent.
Dealt 99,999 damage with a single attack.
Befriended a most unfriendly monster.
Defeated a powerful enemy on equal terms.
Obtained the highest possible result in the battle to determine the fate of the world.