What are Runes? Where are they located?
Runes are universal cosmic constants that, in the universe of Earth-X, can be 'drawn down' by certain practices, to temporarily assume the powers and station of a Runetitan.
As to 'where' Runes are, they're not 'anywhere', being psi-charged symbols that permeat the entire Earth-X universe!
Who 'wrote' the Runes?
He-who-is-now-Dead, of course! Only HE could scribe celestial truths in psi-resonant lettering, as it requires as close to genuine omnipotence and genuine omniscience as is possible. (Lesser beings would be overwhelmingly likely to 'foul' the script and thus neutralize any beneficent effect the text may have had...) Placeholder.
How does one draw down a Rune? What is Runemastery?
Runemastery is the ability to draw down one or more Runes. Currently, only superhumans native to Earth-X are able to do so! Placeholder.
What are Runetitans? How do they come into being?
Runetitans are psychic humans who know how to 'drow down' Runes and activate superhuman status within themselves. This can be simulated in a variety of ways, such Alternate Form or Normal Identity. Placeholder.
Do Runes function outside of the Earth-X universe or Earth-X's Resonances?
Yes. Er... Well...sort of. Placeholder.
You say there're 'regular' psychics on Earth-X? What're they like? How do they differ from Runetitans?
All Runetitans are psychic, but most psychics are NOT Runetitans! Placeholder.
What're the Apkallu, Starvampires and Tlolkku doing on Earth-X?
What are the Sungods doing, on Earth-X?