Hadel:
I know you have heard the master’s call. Only a part of his soul was free but the rest remains by the seal of light within the Disconnected Labyrinth of the Ruins of Ye Sagira. The ghost of the Ancient Giant King, Harnak's Wraith, serves as the warden of the prison where Hermuncus is held. You will face the ghosts of giants corrupted by the light. Defeat Harnak and the seal will be completely broken freeing the soul of Hermuncus.
Once Hermuncus has been freed, he will instruct you on how to acquire the power that the ancient giants once used.