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