Thanks to xris for creating the thread. I originally posted this theory in Generic Discussion:
After ep 6 we have more evidence that the Emperor has his powerbase on the planet
Jupiter. WTF, I hear you cry. Well take a look...
Spoiler for OP:
Ruins floating in the clouds of Jupiter (note 'teleportation' platform):
Jupiter's red spot:
In ep 6 we actually see the Emperor there:
There's also evidence from ep 1 that the power of Geass maybe linked to Jupiter:
Spoiler for ep1:
Mysterious silver planetoids:
Emperor in the ruins on Jupiter talking about 'Ragnarok'. The symbols on the guards clothing is similar to the 'V' shaped emblem on C.C's head:
C.C's mysterious race:
So my theory is that the power behind Britannia, possessed by the Emperor himself is the true power of C.C's people, linked to this mysterious location on Jupiter. This power may well have been stolen from C.C's people and perhaps this is why C.C may be helping Lelouch to tackle Britannia. However C.C being the least trustworthy character in the show, probably has much more involvement than that.
P.S I think Tanaguchi must have a thing for Jupiter, as it also features in Planetes predominantly.
Ragnarok
The Emperor also speaks of 'Union of Ragnarok' in ep 1. Ragnarok in Norse mythology is the 'Doom of the Gods' (Gotterdammerung) in which the gods are overthrown by aggressors lead by Loki. Loki is a trickster, a master of disguise and deception.
In Code Geass, the Emperor could be Odin, the father of the Gods. Valhalla (Odin's Hall of the Dead) could be Jupiter. With Balder (Odin's second son) being Clovis. The Emperor may have been speaking to Clovis on Jupiter in ep 6. Valhalla is the resting place of fallen warriors. Also in Norse legend Loki kills Balder by use of trickery.
Lelouch = Loki?