Scarlet Medal Achievement in Final Fantasy XIII-2
Defeated a powerful enemy with graceful poise.
How to unlock Scarlet Medal
This achievement requires a 5-star rating in the battle with Atlas (Weakened Version) in Episode 2, Bresha Ruins AF005. This can be done on Easy difficulty to save a bit of stress. Note that you do not need to get a perfect Cinematic Bonus to unlock the achievement, though you will need it for "Trigger Finger" and "Defragmented."
You can use the Time Reversal option to attempt this battle again if you do not get it your first try - come back after completing the main story and it will be extremely easy.