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