Theory of the Shadow [SPOILERS.]

[Sexbad]

The Tin Hinan tale (the Mother of Us All) is actually quite unrelated, I believe. The orbs are actually part of an ancient religion known as Mithraism. Agrippa mentions it, too. I'm not incredibly familiar with its workings, but it was based around seven or eight levels of consciousness, to procure an orb being means to get to a higher level.

I don't think Tin Hinan had anything to do with such a religion (but if she did, you're probably right about her guarding of the orbs), so whatever is protecting the orb is probably some God of Mithraism or perhaps someone on one of these higher levels of consciousness. Either it's that or just a radioactive pseudoplasmodium.