Here is the full list of all 55 Omega Quintet achievements.
Reached the game's ending.
Finished Episode 8.
Finished Episode 7.
Maximum hit count exceeded 200.
Maximum damage exceeded 100,000.
Finished Episode 6.
Finished Episode 5.
Defeated 1,000 enemies.
Maximum hit count exceeded 100.
Defeated an enemy with an Extra Chain.
Cleared the Training Facility [1st Floor].
Defeated an enemy with a Harmonic Chain.
Generated a Link Bonus.
Generated a Follow Bonus.
Fulfilled a Request.
Activated Live Concert Mode.
Activated Voltage Gauge Level 5 during Live Concert Mode.
Finished Episode 4.
Finished Episode 3.
Used the PVS.
Finished Episode 2.
Defeated 100 enemies.
Succeeded in executing Overkill.
Finished Episode 1.
Defeated an enemy with a Special Skill.
Maximum damage exceeded 10,000.
Obtained all trophies.
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 10,000 enemies.
Finished Episode 9.
Reached the true ending.
Fulfilled 100 Requests.
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.