Kōsaka

The Kosaka, also written with the characters for Takasaka, were a Shinano warrior house of the Shigeno clan, descended from Sadayuki of the Nezu family; their name came from Kosaka in Saku district. The first head Munekiyo is thought to have become a newly appointed jito after the Jokyu War of 1221; the family acquired its seat at Makinoshima around 1260.

In 1336 the sixth head Shinkaku raised the Southern Court banner at Maki Castle alongside remnants of the Hojo. The rising was put down, though the castle held.

During the Takeda conquest of Shinano Munishige submitted to Takeda Shingen, but was executed at Kaizu Castle in 1561 on suspicion of dealing with the Uesugi, ending the direct line. Kasuga Toratsuna, who married a Kosaka daughter, inherited the name as Kosaka Masanobu. Cadet lines served the Uesugi and Hoshina.