The Hanakura Conflict (Hanakura no ran) occurred from 5/25 to 6/10 of Tenbun 5 (1536) as a succession struggle within the Imagawa clan, the sengoku daimyō of Suruga Province, following the death of their lord, Imagawa Ujiteru. Hanakura was the place name from which Genkō Etan raised arms. He was the younger brother of Ujiteru born outside the line of succession. The conflict came to an end after Sengaku Shōhō, another younger brother of Ujiteru and lineal heir of Ujichika, prevailed and became the successor. Shōhō later became known as Imagawa Yoshimoto.
The Imagawa were relatives of the Ashikaga clan. In 1476, after Imagawa Yoshitada died in battle in Tōtōmi, a dispute erupted within the family between members of the family and influential hikan, or servants, in regard to the issue of succession. In 1487, through the mediation of Ise Moritoki (a liaison for the bakufu later known as Hōjō Sōun, founder of the Gohōjō clan), Imagawa Ujichika became successor as head of the clan.
With the support of Moritoki, a deputy military governor, Ujichika endeavored to strengthen his control over the clan. He enacted a set of provincial laws known as the Imagawa kana mokuroku, establishing his command over family affairs. To prevent internal discord in the wake of his own death, he designated Ryūōmaru (his lineal heir later named Imagawa Ujiteru) as his successor, and, in 1523, invited Taigen Sessai from the Kennin Temple in Kyōto and assigned him to raise his fifth son, Hōgikumaru (the third son of Ujiteru’s formal wife, Jukeini, later known as Sengaku Shōhō and then Imagawa Yoshimoto). In 1525, Ujiteru had Hōgikumaru enter the priesthood whereby he entered the Zentoku Temple in Seko in the Fuji District of Suruga. Ujichika died in 1526 and was succeeded by Ujiteru as head of the Imagawa family.
During Ujiteru’s tenure, the Imagawa reconciled with their rival, the Takeda of Kai Province, and the clan established a consultative system among family members and hikan, or lower-level officials, to manage provincial affairs. However, after the Matsudaira clan gained influence in Mikawa Province, Ujiteru was on the defensive so he abandoned the territory and made plans to invade Kai. He then called upon his younger brother, Shōhō, who, together with Sessai, was practicing Buddhism in Kyōto.
On 3/17 of Tenbun 5 (1536), Ujiteru, along with Hikogorō (his younger brother who was designated as first in the line of succession) suddenly died. Ujiteru’s widow, Jukeini, wielded considerable influence in the family. Together with Sessai and senior retainers, she had Shōhō return to secular life and, after receiving one of the characters from the name of Ashikaga Yoshiharu, the twelfth shōgun, Shōhō adopted the name of Imagawa Yoshimoto. Jukeini and her supporters then settled with the Takeda of Kai and attempted to have Yoshimoto serve as the successor. However, the Fukushima who served as influential servant in the family in charge of military and diplomatic affairs with respect to Tōtōmi and Kai provinces, opposed having Yoshimoto become the next head of the clan. Instead, the Fukushima backed a maternal relative named Genkō Etan. Etan was the son of one of Ujichika’s consorts who was a daughter of Fukushima Sukeharu.
On 5/24, Jukeini met with Fukushima Echizen-no-kami, an advocate for Etan, and attempted in vain to persuade him to change his mind. On 5/25, supporters of Etan raised arms from Mount Kunō, attacking the Imagawa residence in Sunpu. The defenders stiffly repelled the attack, whereupon those backing Etan continued their resistance from Kata-no-kami Castle and Hanakura Castle, garnering support from others in Tōtōmi Province.
Meanwhile, Yoshimoto received support from the Gohōjō clan of Sagami Province, with Okabe Chikatsuna attacking and capturing Kata-no-kami Castle on 6/10. Next, the forces launched an all-out assault against Hanakura Castle where Etan had sought refuge. Unable to withstand the attack, Etan fled and committed seppuku at the Fumon Temple in the Sedo Valley. After the battles in Tōtōmi came to an end, Yoshimoto announced his own succession and then endeavored to tighten his grip on the clan.