Mystic's Memory, Banha's Tears #2

Numbly, I let myself sink into the dark waters. I let out a final breath, preparing to die. A strong pulse of dark blue light blinded my eyes. The light grew stronger and stronger, and my senses returned to me.

The source of the light was a dull gem that I happened to be carrying with me. I received the gem on the same day I left for distant lands. I was holding Master's hand as we got on a boat embarking on such a journey, when someone slipped the gem into my other hand. What I thought was just an ordinary blue stone gave out such a bright blue light that I was suddenly able to see around the pitch dark ocean around me.

I became curious. Who was that person, and why was I given this gem?