A Guardian associated with a City Faction called "The Symmetry", who held beliefs that the Vanguard described as dangerous.1
Ulan-Tan's thesis seems to cover a number of points:
- Light and Darkness must co-exist, and one balances the other in a symmetric relationship.2
- All Light is connected "across space and time", which would presumably also apply to Darkness.3
- The Traveler sacrificed itself for humanity, and it is now up to humanity to return this good deed by healing the Traveler.
Ulan-Tan's relationship with the The Symmetry is not well documented.