The Ko-Mihara school was founded by Masaie during the Kamakura period FROM TOKUJI (1306 TO SHO-CHU 1334 AD. BLADES OF THE EARLY KO-MIHARA SCHOOL ARE FOR THE MOST PART "O-SURIAGE". THIS IS DUE TO THERE GREAT LENGTH THAT GAVE THE MOUNTED WARRIOR A DISTINCT ADVANTAGE. MASAIE AND MASAMITSU WERE succeeded by, Masahiro during the Nambokucho period. Works by Ko-Mihara have strong Yamato influence, AND OCCASIONALLY BIZEN INFLUENCE. IT IS THOUGHT THAT MASAIE SPENT SOME TIME STUDYING With THE MASTERS OF BIZEN, ON HIS WAY TO BINGO (BINGO PROVINCE IS SYNONYMOUS WITH THE MIHARA SCHOOL). Masaie's MOST PROLIFIC PERIOD is thought to be THE Kem-mu era (1334). It is very rare to see any works from Masaie or Masahiro, and are only a few that are dated. All of the MAIN LINE MIHARA smiths signed with Masa; (Masakiyo, Masamitsu, Masanobu).  IN ADDITION TO THE MAIN LINE there was THE "HOKKE ICHIJO", AND SHIMBO MIHARA GROUPS. DURING THE later Nambokucho period several additional mihara groups, SUCH AS ASHIDA, TOMO, KINASHI, SHIMBO HOKKE, AND KAI. these later groups also have  yamato influence. 

The workmanship (kitae) of Mihara blades have high, and wide shinogi-ji, hada with dense ko-itame sometimes with masame, whitish jigane, and hamon styles of suguba sometimes with mixed midare, ashi, inazuma and sunagashi. the most easily noticed distinguishing factor, is the "mihara boshi". these are the most noticeable.

THE TYPICAL "MIHARA BOSHI": THESE BOSHI'S HAVE A RATHER SOFT KO-MARU (SMALL ROUND) TURN BACK, WITH A RATHER ABRUPT TURNED UP (TOWARD THE MUNE) ENDING (SEE DRAWING). Horimono is very rare. ko-mihara blades are rated "OWazamono" (supreme sharpness)!

There is a famous tachi named "O-Mihara" that Toyotomi Hideyoshi, (personal assistant to Daimyo Oda Nobunaga) gave as a gift to Asano Yukinaga, a famous Toyotomi retainer. As for the timeline of this school, Ko-Mihara refers to the early works (LATTER PART OF KAMAKURA), CHU-MIHARA TO THOSE OF NAMBOKUCHO, and Sue-Mihara to THOSE AFTER O-EI (1394) AND during the Muromachi period.

THE EXTREME SHARPNESS, AND DURABILITY OF THE MIHARA BLADES WAS RESPONSIBLE FOR THERE POPULARITY. IT IS COMMON AMONG SWORD JUDGES TO CALL A BLADE WITH YAMATO INFLUENCE THAT THEY ARE UNCERTAIN OF, "MIHARA". early KO-MIHARA BLADES, SUCH AS THIS JUYO EXAMPLE EXHIBITING KAMAKURA STYLE, YAMATO INFLUENCE, AND THE "MIHARA BOSHI" (not always present), ARE VERY DESIRABLE.