A young samurai, Hojo Yoshitoki, was living peacefully with his elder brother Munetoki and sister Masako in the province of Izu. This peace was broken when Minamoto no Yoritomo sought protection from his jailer Ito Sukechika.
Ito Sukechika tried to kill Minamoto no Yoritomo, with the assistance of Oba Kagechika, a powerful local ruler, but the Hojo family decided to protect Minamoto no Yoritomo (called Sukedono for his former position in the Kyoto court).
Minamoto no Yukiie, Yoritomo's uncle, suddenly visited Izu, urging Yoritomo to start a rebellion against the ruling Taira clan under order from Prince Mochihito (who had been killed in a battle immediately after issuing the order).
In August 1180, Minamoto no Yoritomo finally decided to start the action by attacking Yamaki Kanetaka, mokudai (deputy governor) of Izu Province. The night attack was a success, marking the first step in the Genji campaign against Taira.