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