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