Kawachi Daijo Masahiro (正広), the first-generation smith of this name, was the son of Yoshinobu. His earliest signature was Masanaga (正永), changed to Masahiro in 'ei 2 (1625). Though tradition holds that he received the title Kawachi Daijo in 'ei 5 (1628), extant works bearing that title appear only from the eighth month of 'ei 18 (1641), and recent scholarship favors the later date. He died at age fifty-nine in 5 (1665). The consistently identifies him as the most technically accomplished among the so-called soba- smiths -- those working alongside but outside the main line. After the death of the first-generation , he assisted the second-generation Tadahiro and "was highly active as an able collaborator." His son, the second-generation Masahiro, was born in 'ei 4 (1627), initially signed as Masanaga, received the title Daijo in Manji 3 (1660), and upon his father's death succeeded to the name Masahiro and the title Kawachi no Kami. He died in Genroku 12 (1699) at age seventy-three.
Where the main line excelled in , Masahiro "favored -ba," and the describes his signature style as tempering in which is mixed with and . His forging consistently shows tightly packed with extremely fine adhering thickly "in a dust-like distribution," producing the characteristic (rice-bran texture), together with fine . In -ba, the is deep, thick adheres, gathers in the valleys of the , and and run through the , producing a that is repeatedly described as "bright and clear." A straight at the base is noted as a feature "often encountered among various soba- smiths." In the first generation's rarer works, the attaches "evenly without patchiness" and the is "bright and clear" -- demonstrating, as the notes, "the high technical ability of the first-generation Masahiro not only in -ba but in as well." The second generation produced both modes but "was particularly adept at -ba," and his works are distinguished by the inclusion of round-headed and -like elements within the irregular temper.
The describes the first-generation Masahiro's finest -ba as tempering of "pronounced rises and falls, with abundant throughout the and a flamboyantly undulating pattern that is richly animated by conspicuous ," yielding blades "brimming with martial spirit and power." His are singled out for of exceptional length and prominence, and his early works are noted for being "even more florid than usual" with abundant internal activities. The second generation's characteristic contribution is the manner of mixing -like elements and round-headed into the temper -- a distinctive feature of his approach to -tori (temper pattern conception). Both generations share the hallmark of bright, vivid and , and both are praised for works that are -- sound and well-preserved. Dated works by the first generation are "encountered only in small number," making inscribed examples of particular documentary value for the study of this foremost soba- master.