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