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