Here is the full list of all 12 AIRIS achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Achieved Everea's Hidden Ending: AI-ris
Achieved Everea's Ending #3: Back to the Start
Achieved Everea's Ending #1: The Real Everea
Achieved Everea's Ending #2: Joint Worlds
Achieved Lyall's Hidden Ending: Eternal Loop
Achieved Lyall's Ending #3: Bliss in Ignorance
Achieved Lyall's Ending #2: Pariahs in Love
Achieved Lyall's Ending #1: New World, New Life
Achieved Kylan's Ending #3: Warrior's Sacrifice
Achieved Kylan's Ending #2: You Are My Home
Achieved Kylan's Hidden Ending: Just Deserts
Achieved Kylan's Ending #1: Worlds Apart