Here is the full list of all 55 Omega Quintet achievements.
Completed archives.
Finished all Quests.
Hunted 10 MADs with Takt's pursuit.
Used group defense 100 times.
Fulfilled 100 Requests.
Defeated Double X.
Cleared the Training Facility [12th Floor].
Cleared the Training Facility [11th Floor].
Cleared the Training Facility [10th Floor].
Cleared the Training Facility [9th Floor].
Cleared the Training Facility [8th Floor].
Cleared the Training Facility [7th Floor].
Cleared the Training Facility [6th Floor].
Cleared the Training Facility [5th Floor].
Maximized proficiency in all 5 Mic types with any one character.
Reached the true ending.
Reached the game's ending.
Reached the true ending in Advanced mode.
Finished Episode 9.
Finished Episode 8.
Used pair defense 100 times.
Finished Episode 7.
Defeated 1,000 enemies.
Finished Episode 6.
Activated Voltage Gauge Level 5 during Live Concert Mode.
Maximum damage exceeded 1 million.
Maximum hit count exceeded 300.
Finished Episode 5.
Defeated an enemy with a Special Skill.
Defeated an enemy with an Extra Chain.
Cleared the Training Facility [1st Floor].
Maximum hit count exceeded 200.
Maximum damage exceeded 100,000.
Fulfilled a Request.
Activated Live Concert Mode.
Finished Episode 4.
Finished Episode 3.
Defeated an enemy with a Harmonic Chain.
Generated a Link Bonus.
Maximum hit count exceeded 100.
Generated a Follow Bonus.
Finished Episode 2.
Defeated 100 enemies.
Used the PVS.
Succeeded in executing Overkill.
Finished Episode 1.
Maximum damage exceeded 10,000.
Obtained all trophies.
Otoha reached max affection.
Kyouka reached max affection.
Kanadeko reached max affection.
Nene reached max affection.
Aria reached max affection.
Defeated 10,000 enemies.
Approval rating exceeded 1 billion.