Here is the main story setting i have noted down for my craftworld and how they have come into existence. Bare in mind its really early produciton and was noted down in about an hour in all, so is not 100% set in stone. l think?
Fluff
Ulthwe plan on attacking the chaos space marines by using the webway to travel right into the eye of terror. They send out a scout force consisting of 40 guarian defenders, with a variety of heavy weapons platforms and 30 storm guardians all of which have warlocks present to boost their morale. Supporting the guardians are 2 squadrons of vypers armed with shuriken cannons and brightlances (incase of any heavy machinery).
Whilst travelling through the webway, they encounter an unfamiliar discovery (not sure yet). Investigating this discovery, they discover a loop hole within the webway. Falling down this loop hole, they discover a planet beneath them.
Landing on the planet they realise that its empty. Their was nothing but flat ground in sight. The texture of the planet was soft, with a grass like flooring.
The eldar went back to Ulthwe and told them about this discovery, in which they sent in the seer council to investigate more. After investigation, the seers gave the place the all clear, and deployed multiple units consistsing of guardians, a few warlocks and newly recruited seers and bonesingers.
As time went on, the bonesingers built a new eldar society, consisting of many buildings and eventually a large population cap (not as high as others of course, but high to the eldar).
Over time the eldar explored of the planet with their cruise ships and encountered the other craftworld. This began a trading system with them, for they would enlighten the other craftworlds with more information about the webway, in return for there usefulness. This lead into the craftworld getting aspect shrines from the Beil-tan, Their own infinity circuit separate from Ulthwe from Iyanden, many rangers came to protect the planet from Alaitoc and Jetbikes were able to then be produced on the planet thanks to the saim hann.
However being in the webway, they did encounter the harlequins who became well known to appear for them, for they live in the webway also. Because of this they use a lot of harlequins, along with aspect warriors and guardians. However being from Ulthwe, and originating from Ulthwe Guardians are seen as the most important units, for all the others are simply deployed to support the guardians.
Ulthwe had decided that once the Great War is over, this is where they can go to rest and live life onwards.
C+C welcome