The Decadence (The Decadent Empire) - Big rich empire that doesn't want to exist

Rapid Expanders, bad at exploiting their territory.

Faction-specific traits:

- Decadent empire: Start with an additional colony ship. Colony ships can travel through wormholes right from the start. Every system apart from the capital produces -50% FIDSI and half of expansion disapproval. This penalty only exist for Decadence, if other faction gets the colony the penalty is gone.

- No reason to fight: The Decadence spaceships have a penalty to their attacking possibilities outside of empire territory.

- Pearl of the Universe: has a small bonus to researching any technology any known faction had already researched.

- Defend from barbarians: whenever you fleet fights in their own system local planets contribute additional small ship ignoring the supply limit.

The Government: Celestial Empire. The emperor rules over the Decadent Empire, but his rule is weak, the system is conservative and is resistant to change. Faction-specific quests may involve reforming this system.

The planet: Capital planet is huge and has a great anomaly allowing for a very strong core system.

(The Decadence is similar to the idea I've posted for Endless Legend so if some of you think it's familiar then you've seen that thread)

The Decadence unites species and planets that have remained alone in the universe without Endless. By the time other factions started conquering the stars The Decadent Empire lost all sense of meaning and became weak. It's big, old and wealthy but small part of it riches goes to a good cause instead of local corrupted rulers. It can defend from attacks of upstart races but can no longer mobilize itself to properly deal with rising menace along its borders.

Gameplay-wise The Decadence rapidly expands at the beginning of the game. Due to its size it has lots of resources and territory but it's limited in a real production. It can compete by researching mostly the stuff others have researched and trading resources for technologies. It also relies on a very strong core system. AI personality of The Decadent Empire is very defensive, like to buy technologies and is more eager to trade away his planets. They have two prefered ways to victory: either turning their starting size into a good enough advantage so that their big fleets are able to conquer even with their subpar fleets. Or with good enough technologies (perhaps with faction quests lowering the -50% FIDSI penalty for non-capital system) they can become an economic powerhouse. Either way requires working against your limitations.

You have some good ideas here. I especially like the unique 2 colony ship idea. However, I'm not sure how this all fits with the lore of them being an already established and old empire.

Also, you mention that they tend to win either with big fleets or an overpowering economy, both of which don't quite fit the theme of "pacifist diplomats". Could you make some changes to guide this faction in the correct direction?