Muramasa Senji

A swordsmith from Ise Province, Kuwana. Muramasa is a famed blacksmith within Ise Province. His title by the time of the Bunki era is Uemon-no-jō. He is said to be the founder of the swordsmith school which made the sharpest katana in the Sengoku era.

Muramasa also theorized that he was summoned in Emiya Shirou's body because Shirou has a similar body and mind to that of Muramasa's. Furthermore, he believes Shirou had shared his way of life and experienced a similar end. Muramasa speculates that Shirou could be his descendant.

(Source: TYPE-MOON Wiki)