According to the
April issue of Comptiq magazine, Fate/kaleid・linerプリズマ☆イリヤ (Fate/kaleid liner PRISMA☆ILLYA) a Fate/stay night alternate universe spin-off manga by Hiroyumi Hiroshi (who has previously drawn Fate doujins under the circle KALMIA) will be receiving an anime adaptation.
Spoiler for synopsis:
A two-volume manga series that introduced the story. Deals with Illya becoming the Magical Girl and having to collect Class Card together with Miyu.
Rin and Luvia were originally Magical Girls that were supposed to collect the Cards, but after trying to use Class Cards in a quarrel, Kaleidosticks abandoned them (mid-air) and went on to independently search for new masters. Ruby made a contract with Illya, and Sapphire with Miyu.
After a series of battles, Illya and Miyu were able to collect all Cards and became good friends, while Rin and Luvia remained in Japan by the order of Zelretch.
Spoiler for synopsis for 2wei:
A second story (five volumes) that focuses on a new character, Kuro, who is a girl identical to Illya, except for darker skin, that emerged from Illya after her failed attempt to use Archer Class Card. Kuro has been shown to act extremely antagonistic towards Illya.
In the same advertisement the third story was announced as "3rei"
More information at the
Official Anime Site (japanese),
aniDB entry (english) and...
Sources: Moetron blog and
TM@wikia