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