Born in 1434, Ashikaga Shigeuji became the 5th Kamakura Kubo in 1447, but relations with the Kanto Kanrei Uesugi clan deteriorated. In 1455 he had Uesugi Noritada murdered at his residence, igniting the Kyotoku War. Unable to hold Kamakura against the Uesugi counterattack, he moved his base to Koga in Shimosa Province, entering the newly repaired Koga Castle in 1457. Thereafter known as the "Koga Kubo," he ruled the Kanto region from Koga Castle for roughly forty years. In 1483 he reached a settlement with the shogunate (the Tohi Gattai) that confirmed his status as Kubo while formally abandoning any return to Kamakura. He died in Koga in 1497 at age 64. His descendants — Masauji, Takamoto, Haruuji, and Yoshiuji — continued the Koga Kubo line for about 130 years.

Having lost his father and brothers to conflict with the shogunate in his youth, he spent his life contesting the Kanto Kanrei Uesugi clan. He combined the resolve to relocate his base from Kamakura to Koga with the governing skill to sustain the Koga Kubo regime for some forty years.

He established Koga Castle as the seat of the Koga Kubo for roughly 130 years and laid the foundations of the town of Koga. The Koga Kubo lineage passed down through his descendants Masauji, Takamoto, Haruuji, and Yoshiuji, profoundly shaping the Sengoku-era history of the Kanto region.