Here is the full list of all 25 Ereban: Shadow Legacy achievements.
Obtain the Ghost medal in every chapter
Unlock the Hope Ending
Complete Chapter VI
Complete Chapter V
Help Gerel escape with his cell in Chapter IV
Complete Chapter II
Complete Chapter I
Unlock the Light Ending
Unlock the Darkness Ending
Obtain the Ruthless medal in every chapter
Obtain the Merciful medal in every chapter
Obtain a 'S' rank in every chapter
Learn all the non-lethal and mixed shadow powers
Learn all the lethal and mixed shadow powers
Craft and improve every gadget
Help Kelsa and all her team in Chapter III
Help Helena to find out what happened to her family in Chapter V
Open the secret room in Chapter VI
Use Shadow Control on a worker
Paralyze three or more SYMs with a single mine
Use Shadow Vortex on three or more enemies in a row before materializing
Use Shadow Merge to avoid a HAWK shot
Scan the crow in Chapter III with the visor
You are now part of the creed
Get detected by three or more SYMs at the same time