沼地の洋館で、
一人の傭兵がサーヴァントの召喚を行う。
青年のコードネームはシグマ。

通常の聖杯戦争では召喚し得ない、
あまりに特異な英霊を喚び出した彼に、
突如『最初の試練』が訪れる―――

In a mansion situated in a swamp, a lone mercenary summons a Servant. His codename is Sigma.

He has called forth a singularly unique Heroic Spirit that could never be summoned in a normal Holy Grail War. And suddenly, he encounters his first trial...