Born in 1447, Sagara Tametsugu was the 12th head of the Sagara clan, based in Hitoyoshi in Higo Province. In December 1483, with reinforcements from the Shimazu, Hishikari, and Kitahara clans, he launched an attack on Fumoto Castle (later Furufumoto Castle), held by Nawa Akitada in Yatsushiro. He captured it the following year, 1484, pacifying Yatsushiro and greatly expanding Sagara power from Hitoyoshi into the Yatsushiro region. The Sagara clan subsequently held Furufumoto Castle as their base for controlling Yatsushiro for roughly a century afterward. He died in 1500.

A commander with the diplomatic skill to secure cooperation from neighboring powers (the Shimazu, Hishikari, and Kitahara clans), achieving a conquest of Yatsushiro that would have been difficult alone. A man of real capability who greatly expanded his clan's sphere of influence.

Tametsugu's conquest of Yatsushiro established the Sagara clan as a powerful warrior house controlling territory from Hitoyoshi to Yatsushiro in southern Higo. The ruins of Furufumoto Castle were designated a National Historic Site in 2014, together with Yatsushiro Castle and Mugishima Castle, as the "Yatsushiro Castle Sites."