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.
Defeated the Hermit.
Unlocked access to the remaining Major Arcana.
Maxed out one Social Stat.
Accepted an invitation to hang out five times.
Defeated the Chariot and Justice.
Triggered a skill change during fusion.
Aced an exam.
Nursed a cat back to full health.
Maxed out one Social Link.
Defeated the Hierophant and the Lovers.
Unlocked a teammate's Combat Characteristic.
Performed a fusion with three or more Personas.
Harvested a crop that you grew with a teammate.
Rescued a missing person.
Spent an evening in the dorm with a teammate.
Used a total of 50 Twilight Fragments.
Defeated the Empress and Emperor.
Obtained 10 Personas during Shuffle Time.
Obtained 10 Major Arcana during Shuffle Time.
Earned over a total of 50,000 yen from part-time jobs.
Ordered from a secret menu at the Iwatodai strip mall at night.
Obtained an item from a Persona Conception.
Initiated 50 Chance Encounters.
Defeated the Priestess.
Opened 50 treasure chests.
Performed 50 All-Out Attacks.
Performed a Dyad Fusion.
Defeated a rare, golden enemy.
Performed a Shift.
Joined the Specialized Extracurricular Execution Squad.
Obtained Orpheus.
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.
Maxed out all Social Stats.
Acquired every Twilight Fragment in town.