Mutsu no Kami is the third generation of the main line at Saga, the eldest son of the second-generation Ōmi no Daijō Tadahiro. Born in Kan'ei 14 and called Shinzaburō, he received the title Mutsu no Daijō in Manji 3, became Mutsu no Kami in 1, and died in Jōkyō 3 at fifty, seven years before his father. The name came to him because, after the death of Tosa no Kami , that house returned it to the main line. The published sources explain the comparative scarcity of his work by a short career and by his service for his long-lived father, his works being few "because he served as a substitute maker for his father".
His characteristic manner is a , the temper the published sources call the one "he most excelled in". It is tempered with deep and well-adhered , small entering, fine and running through it, and a bright, clear . The is typically long, wide and thick, with a deep and an extended , heavy in the hand. The judges read this shape as his grandfather's rather than his father's, "calling to mind not the father but rather the grandfather, the first-generation ". The is a that turns back deeply and stops firmly toward the , and the published sources single this out: "the of the is deeper than in the first and second generations".
His reputation rests above all on the . A packed tightly, with fine and thick, takes on the rice-bran of , and enter finely to give it strength. The published sources call his forging "the strongest and most refined of the upper three generations" and name it his true hallmark, "the excellence of his forging is his true hallmark". On one they go further, finding the fine activity of a edge "to the degree of surpassing the first generation".
The record falls into distinct groups that the published sources themselves draw. An early group is placed by the shape of the tip, judged "an early work of this smith from the tip and the manner of signature"; even these already show the strong and the deep . Beside the stands a register. His own mixes , angular and pointed elements, small in pattern and with some rise and fall, and "small at the heads are often seen". On some he tempered his father's ashinaga-, and on one the pattern is "to be mistaken for the of his father Ōmi". Dated works are scarce: the published sources state that "dated works by this smith are extremely rare", and they treat his 2 and Enpō 4 blades as documents of his signature.
Part of his record carries his father's name. Five blades signed no ju Ōmi no Daijō Fujiwara Tadahiro are judged by the to be his work, each concluding that "this sword is perceived to be a substitute work of the third-generation ". The evidence is his own hand: a smaller and livelier than the father's orderly ashinaga-, finer and thicker with more prominent , a deeper , shallow file marks and the chisel of the signature. The published sources value them as material "for knowing the work of the third generation as substitute maker for his father the second-generation Tadahiro". He is also the maker of a rare with the second-generation Masahiro, which the published sources call unique: "a joint work of the third-generation and Masahiro is not seen apart from this sword".
Two further judgments shape his record. A rare signed only with the five characters no is attributed to him rather than to the founder, by the chisel of the signature, the position of the and the workmanship; the published sources note that "the five-character signature of this smith is extremely rare". They also caution that the main line signs on the in the position, so that a signature in the position "calls for particular care regarding authenticity".
Fujishiro grades him Jō-jō . He has no National Treasures or Important Cultural Properties on record; his standing rests on nine blades in the rank and some fifty in the , with two blades in the Imperial collection. Several of the are called his finest workmanship, one of them "transmitted in the Nabeshima family in the domain era", the house his line served. Signed blades of Mutsu no Kami survive in real numbers and a example reaches the market from time to time, while his finest komenuka come to light only rarely and are a landmark when they do.