Here is the full list of all 27 Keeper of the Sun and Moon achievements.
Attack a foe the human way.
Become a hunter.
Be killed by hunters.
Stop the destruction of a building.
Be mind controlled by a foe.
Release an old foe.
Never use compulsion.
Almost die in the final battle.
Easily win the final battle.
Have a bountiful winter solstice.
Get high marks for the first semester.
Kill Davina's hellhounds.
Learnt that Kol was threatened by Reyna.
Learnt that Gisela and Yakov are cousins.
Learnt that Jarrod is a hunter.
Learnt about Astrid's connection to Reyna.
Learnt that Altair compelled Astrid.
Learnt that Gisela is blackmailing Celosia.
Learnt that Katia has amnesia.
Learn the identity of the new keeper.
Learnt about Reyna's motivations.
Learnt about the thief's intentions.
Learnt the purpose of the Constellation Project.
Learnt about your connection to the Constellation Project.
Learnt why your parents hate magic.
Learnt who your father is.
Learnt that your mother was a nymph.