It is gained automatically after listening to the conversation option "Eirena's Journey" with Eirena.
It reads as follows:
I felt no fear when they sealed the tomb before me, only a sense of peace as my mind drifted away into the darkness. It seems I opened my eyes only seconds later and beheld the chamber in ruins, half-buried in sand. I have left everything behind... Only hope guides me now. — Eirena