Lifespan: 1/7 of Kanshō 3 (1462) to 7/18 of Kyōroku 4 (1531)
Title: Director of the Cavalry of the Left Division
Bakufu: Second Koga kubō of the Muromachi bakufu
Clan: Ashikaga (Koga kubō in the Kantō)
Lord: Ashikaga Yoshiki → Ashikaga Yoshizumi → Ashikaga Yoshiharu
Father: Ashikaga Shigeuji
Mother: Daughter of Yanada Naosuke (Denshinin)
Siblings: Masauji, Yoshitsuna (Uesugi Akizane – may have been a son), Teigan Shōei (may have been a son)
Children: Takauji (Takamoto, Yoshimoto), Yoshiaki, Motoyori, Sadaiwa
Ashikaga Masauji served as a bushō during the Sengoku period and as the second Koga kubō.
Masauji inherited the role of Koga kubō from his father, Ashikaga Shigeuji, in 1489. Similar to his father, Masauji received one of the characters in his name from the shōgun, Ashikaga Yoshimasa. During the Chōkyō Conflict, a prolonged power-struggle between Uesugi Akisada (the deputy of the Kantō Region and head of the Yamauchi-Uesugi clan), and Uesugi Sadamasa (the head of the Ōgigayatsu-Uesugi clan), Masauji sided with the Ōgigayatsu-Uesugi. However, following the demise of Uesugi Sadamasa, the clan weakened, whereupon Masauji switched his allegiance to the Yamauchi-Uesugi. In 1496, Masauji joined with Uesugi Akisada (of the Yamauchi-Uesugi) against Uesugi Tomoyoshi (of the Ōgigayatsu-Uesugi) at the Battle of Kashiwabara in Musashi Province. In 1504, at the Battle of Tachikawa-no-hara in Musashi, he fought against Ise Moritoki (later known as Hōjō Sōun) and Imagawa Ujichika.
In 1505, after a settlement between the two rival branches of the Uesugi, Masauji arranged for his younger brother, Akizane, to be adopted by Uesugi Akisada. In 1506, he came into conflict with his lineal son, Ashikaga Takamoto, with whom he initially reconciled. In 1510, he had another falling out with Takamoto regarding the issue of succession after Akisada’s death in battle, and also opposed his second son, Ashikaga Yoshiaki. This caused Masauji to become isolated in his palace seat in Oyumi during the Eishō Conflict. After being defeated in his confrontation with Takamoto (who had the backing of the Yanada and Utsunomiya clans), Masauji lost Koga Castle and fled to the Oyama clan for protection.
Masauji was compelled to settle with Takamoto from a position of weakness, assigning the title of kubō to Takamoto, entering the priesthood, and adopting the name of Dōchō. Masauji lost the protection of the Oyama clan and, through the assistance of Uesugi Tomoyoshi, withdrew to a residence in Kuki in Musashi Province. In this location, he founded the Kantō sub-temple on Mount Nagayasu. In 1520, Masauji visited Koga Castle and met with Takamoto. Masauji died in 1531 in Kuki.
In regard to the conflict between the two branches of the Uesugi clan after the slaying of Ōta Dōkan, Masauji followed the path taken by his father, Shigeuji. Namely, he endeavored to maintain the status as the governing military family in the Kantō Region. This approach backfired when he ended up in conflict with his own sons. This later enabled the Gohōjō clan to bring about the demise of the Koga kubō family and steadily advance into the Kantō Region.
During the era of Masauji, the Koga kubō witnessed the peak of its cultural prosperity. In his later years, Inawashiro Kensai, a renga master (a traditional formed of linked-verse poetry) visited Tashiro Sanki, the physician for the kubō family. Poems composed by Kensai for Masauji reveal that Kensai waited upon Masauji. He also presented written works to Masauji, revealing a relationship of a student and teacher between them. Masauji also maintained a relationship with Gyokuin Eiyo, a Zen priest from Kamakura. Based on the laws of the first Koga kubō (Shigeuji), Eiyo visited three times to Koga to assist Masauji. A portrait of Masauji at the Kantō sub-temple in Kuki dated 1521 is inscribed by Eiyo.