On the 27th day of the first month of 1219, returning from his ceremony of installation as Minister of the Right at Tsurugaoka Hachimangu, Sanetomo was struck down by his nephew Kugyo. The 28-year-old poet-shogun was laid to rest in a yagura cave tomb in the hills behind Jufukuji, the temple his mother Masako had founded. When she died in 1225, her own yagura was carved beside his — the end of the Minamoto shogunal house and that of the Nun Shogun resting quietly side by side in the temple woods.

When Sanetomo was assassinated by Kugyo in 1219, Masako lost her second son and saw the Minamoto shogunal bloodline extinguished in three generations. Her grief was said to be unending. By placing her own tomb beside his, she chose to rest with her son for eternity.

The Kamakura shogunate that Yoritomo founded saw its direct bloodline end with his sons — Yoriie and Sanetomo. The yagura of Sanetomo silently tells of both Yoritomo's founding of warrior government and the rapid extinction of his own line within just three generations.