Here is the full list of all 26 Othercide achievements.
Defeat every boss in a single recollection
Activate all Remembrances
Defeat Suffering
Have a level 15 Daughter
Discover all story chapters
Defeat The Child
A Scythedancer has been germinated
Defeat The Maid
Kill 300 enemies
Earn 5 traits on the same Daughter
Defeat The Deacon
Sacrifice a Daughter with one memory attached
Defeat The Surgeon
Close 20 Synapses
Spend 4000 vitae
Sacrifice a Daughter
Lose 400 HP because of reaction or interruption skills
Resurrect one Daughter
Sacrifice a Bright Soul
Add one memory to a Daughter
Start a new Recollection
Save a Bright Soul
A Daughter is killed in battle
Close the first Synapse
Reach the chrono map
Finish the tutorial by defeating all enemies