Master & BERSERKER

A duo formed by a Heroic Spirit, Dimitri, and it's Master, Kotomine Kirei.

TCR Season 1
After the defeat of The Empire, Dimitri Alexandre Blaiddyd left on a mission and marched to Hell to destroy Edelgard von Hresvelg's soul once and for all, so that it could never return. However, the dark ruler of that realm sensed the burning anger that was Dimitri's soul, and decided to add it to his collection of truly unique souls, by using the power of The Grimoire he snatched Dimitri's soul from his body and kept him as his "Caged Beast".

TFR Season 4
When rumors spread of a "Caged Beast", Kirei Kotomine makes his way to hell and vanquishes the avatar of its foul emperor and finds a tortured spirit in the darkest part of this realm. Kirei offers it freedom, at the simple price of a contract...

Thus, using the class container of a BERSERKER for this soul filled with anguish, he forges a contract and the spirit is given physical form, as Kirei's Servant.

Episode 11
After returning from the demonic realm, Kirei offers his assistance to Tohya Hachijo, in repayment to Battler Ushiromiya for at one point being the closest thing he had to a friend. Dimitri is sent against the sentinel senator, Steven Armstrong, to occupy him and Kojima. Even though normally a Servant far outclasses most other kind of beings in sheer defence, the Laws of Wrestling being in effect, a Servant's abilities are far reduced in a formal wrestling ring. Thus, Dimitri was barely defeated by the monstrous congressman.

Lamenting his loss, Kirei told Dimitri that his purpose was fulfilled in stalling Kojima.