Here is the full list of all 48 Persona 3 Reload achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Watched the good ending.
Acquired every Twilight Fragment in town.
Sealed Nyx.
Invited Elizabeth to your room.
Maxed out all Social Links.
Nurtured a romance.
Fused Messiah.
Defeated the Reaper.
Unlocked all Social Links.
Awakened all teammates' ultimate Personas.
Earned over a total of 50,000 yen from part-time jobs.
Defeated the Hanged Man.
Encountered a Dark Zone in Tartarus.
Accepted an invitation to hang out five times.
Defeated Fortune and Strength.
Discovered and conquered 10 Monad doors.
Maxed out all Social Stats.
Dealt over 999 damage in a single attack (All-Out Attacks excluded).
Defeated the Hermit.
Used all teammates' Theurgy.
Unlocked a teammate's Combat Characteristic.
Maxed out one Social Link.
Defeated the Chariot and Justice.
Unlocked access to the remaining Major Arcana.
Aced an exam.
Nursed a cat back to full health.
Defeated the Hierophant and the Lovers.
Maxed out one Social Stat.
Rescued a missing person.
Harvested a crop that you grew with a teammate.
Spent an evening in the dorm with a teammate.
Obtained 10 Major Arcana during Shuffle Time.
Used a total of 50 Twilight Fragments.
Performed a fusion with three or more Personas.
Obtained an item from a Persona Conception.
Defeated the Empress and Emperor.
Ordered from a secret menu at the Iwatodai strip mall at night.
Initiated 50 Chance Encounters.
Triggered a skill change during fusion.
Opened 50 treasure chests.
Defeated the Priestess.
Obtained 10 Personas during Shuffle Time.
Performed 50 All-Out Attacks.
Defeated a rare, golden enemy.
Performed a Dyad Fusion.
Performed a Shift.
Joined the Specialized Extracurricular Execution Squad.
Obtained Orpheus.