[Mr. Guy]

Some questions regarding the Heroic Spirits...

Spoiler:

From what I gather, being Servants in the war for the Heaven's Feel isn't what Heroic Spirits were originally made for. I also gathered that the only reason they're able to be summoned as such is because of the Holy Grail's relationship with the Third Magic. So what is the true purpose of them?

How exactly does one become a Heroic Spirit? And is becoming a Heroic Spirit something that only Earth creatures can do? So we won't see a Type-Mercury Servant or the Crimson Moon, even if they are well known and regarded highly?

*edit* This is also more of a Tsukihime question, but is Primate Murder considered Type-Gaia?