Here is the full list of all 35 Final Fantasy XIII achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Recognized the true threat to the world's future.
Fully developed all characters.
Held every weapon and accessory.
Felled a heavyweight of the lowerworld wilds.
Completed all Cie'th Stone missions.
Earned a 5-star rating for all Cie'th Stone missions.
Triumphed over undying lowerworld souls in seven fierce battles.
Mastered the Saboteur role.
Discovered buried treasure with a little help from a chocobo.
Mastered the Sentinel role.
Mastered the Synergist role.
Mastered the Commando role.
Mastered the Medic role.
Mastered the Ravager role.
Witnessed the dawn of a new crystal legend.
Earned a 5-star rating in the battle to determine the world's fate.
Completed all high-level Cie'th Stone missions.
Completed all mid-level Cie'th Stone missions.
Toppled a green terror and cut an oversized succulent down to size.
Passed Titan's trials.
Dealt 100,000+ damage with a single attack.
Defied destiny's charge and embarked on a different path.
Took over 10,000 steps on the lowerworld surface.
Discerned the full attributes of 100 enemies.
Completed all low-level Cie'th Stone missions.
Traveled to the world below, seeking a way to alter fate.
Took the fight to the enemy's door.
Carried the burden of guilt to the end of the line.
Made plans to infiltrate enemy-occupied territory.
Evaded pursuers, though memories of the past still gave chase.
Resolved to be more than a victim of circumstance.
Slipped through the net and lived to fight another day.
Strode into danger's den and paid the consequences.
Survived the Purge to confront a greater peril.
Took the first steps toward challenging an unjust fate.