Turns out that special disc is a 12 minute digest of a Fate/Stay Night novel which one of the founders of Type-Moon, Kinoko Nasu, wrote in highschool before they even founded the company.
http://yaraon.blog109.fc2.com/blog-entry-6264.html
The cast is entirely different, I'm very surprised how much of a secret this has been kept.
Kana Hanazawa as Ayaka Sajō, Saber's Master
Takahiro Sakurai as a male version of Saber
Yūichi Nakamura as Archer
Kazuya Nakai as Lancer
Chiwa Saito as Misaya Reirōkan, Lancer's Master
Megumi Ogata as Rider's Master
Mamoru Miyano as Rider
Takehito Koyasu as Sankureido Faan
Aki Toyosaki as Aika Sajō
Hiroki Touchi as Sajō's father
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source)