Here is the full list of all 34 Omensight achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Unlock your first Omensight
Defeat Ratika in battle
Unlock the Pygarian Seal
Witness Voden's appearance for the first time.
Unlock your second Omensight
Unlock the last Omensight
Unlock the Rodentian Seal
Unlock Vera's Seal
Unlock the Kladen Seal
Kill 100 Pygarian soldiers
Kill 100 Rodentian fighters
Kill 100 Ciphers
Unlock all bonuses at the end of a day
Kill four enemies with the same column
Kill a surrendering enemy
Use Companion ability 50 times
Use Delay of Fate 20 times
Use Phantom Grasp 50 times
Use Phantom Blast 20 times
Use Lethal Flurry 20 times
Use Phantom Dash 30 times
Throw a bomb towards a column while inside Delay of Fate's sphere
Jump on the head of all your companions
Launch a Phantom Blast on an enemy thrown with Phantom Grasp, while inside Delay of Fates' sphere
Execute two Lethal Flurries in a row
Break a barrel thrown by a Shark while it's in the air, by throwing a barrel at it
Launch 4 Phantom Blasts while inside Delay of Fate's sphere
Unlock all Harbinger's Blade upgrades
Unlock all Harbinger's Aegis upgrades
Defeat Draga in battle
Defeat Ludomir in battle
Defeat Indrik in battle
Imprison Voden
Unlock all other trophies