The current head of the Isemi family, a group of mages seated in the western part of Tokyo.
Their stronghold is on the deep green summit of Mt. Okutama, but he owns several facilities, which focus on medical studies, in the downtown area too.
As a magi family it's rare for them to achieve adaption and conformity to a certain degree for modern science. Although one could say they are compensating themselves with modern science as their circuit linage has been losing it's power it once had.
Fate/Prototype: Fragments of Sky SilverEdit
He manages to summon Rider as his servant for the Holy Grail War by using Nefertari's necklace as a Catalyst, much to Rider's fury, as he is under the impression that the tomb of his most beloved wife was broken in and the necklace was stolen just to summon him.
He dies along with the rest of his clan when Assassin spreads her poison throughout his base on Mt. Okutama.