Shimotsuma Raishū served as a bushō and bōkan, or head of administrative affairs, at the Hongan Temple. Raishū was the eldest son of Shimotsuma Raigen and older brother of Shimotsuma Raisei. He held the Court title of Governor of Chikuzen.
After approaching his maternal grandfather, Renjun (who served as the guardian of Shōnyo, the tenth-generation high priest of the Hongan Temple), in 1528, Raishū headed toward Kaga Province and, together with Jikken from the Chōshō Temple (Renjun’s son-in-law), confronted the kashū-sangaji, or the Three Temples of Kaga, over an issue concerning the seizure of landholdings. The kashū-sangaji were headed by the Kaga Ikkō-ikki who gave nominal recognition to the Togashi clan as military governors of the province but operated on an autonomous basis. The temples included the Matsuoka Temple in Hasadani in the Nomi District, the Kōkyō Temple in Yamada in the Enuma District, and the Honsen Temple in Wakamatsu in the Kahoku District.
In 1531, a conflict arose within the Hongan Temple (whose members were adherents of the Jōdo-Shinshū sect) in regard to reformation of the religious group. This event was known as the Kyōroku Disturbance or, alternatively, as the Dai-shō ikki. From 1532 to 1535, a separate conflict between members of the Hongan Temple on one side and the Hosokawa and Hatakeyama clans on the other side is known as the Tenbun Disturbance. These two sequential events are referred to together as the Kyōroku-Tenbun Conflict.
During the Dai-shō ikki, Raishū associated with the Dai ikki. The Dai ikki were comprised of the Chōshō Temple and the Hongaku Temple who obeyed the orders of the high priest of the Hongan Temple, while the Shō ikki consisted of the Three Temples of Kaga who were branded as rebels and purged for recognizing (albeit nominally) the authority of the kokushu, or provincial lords of Kaga – the Togashi clan.
On 9/26 of 1531, the combined forces of Asakura Norikage (Sōteki) and the Three Temples of Kaga (the Shō ikki) defeated the army of the Hongan Temple (the Dai ikki) at the Tedori River in Kaga. In the eleventh month, however, at a battle in Tsubata in the Kaga District, a crushing counterattack by the Hongan Temple forces led to the death, among others, of Hatakeyama Ietoshi and the fall of the Kyōkō Temple – the last of the Three Temples of Kaga. After this battle, Renkō (the abbot of Matsuoka Temple) was incarcerated and died soon thereafter, while Renkei was executed. Rengo (the abbot of Honsen Temple), Kensei (the abbot of the Kōkyō Temple), and Jitsugo (the abbot of the Gantoku Temple in Kawachi) fled from Kaga whereupon orders were issued to the branch temples and their members across Japan to track and kill them. Six years later, they were formally expelled from the sect on the basis of a plan by former members of the Three Temples of Kaga to attack the Hongaku Temple. Meanwhile, Togashi Taneyasu, a shugo daimyō, was ousted from his position as the military governor of Kaga.
This resulted in a period of governance of Kaga headed by the high priest of the Hongan Temple. Meanwhile, after purging most of his family members, Renjun secured his position by backing Shōnyo as the high priest. Renjun is said to have regretted killing or ousting his siblings and nephews and, while on the verge of his death nearly two decades later, requested that the status of Kensei and Jitsugo be restored.
During the Tenbun Disturbance, the Hongan Temple clashed with Hosokawa Harumoto in the Kinai. After the burning of the Yamashina-Hongan Temple in Kyōto, Shōnyo moved to the Ishiyama-Hongan Temple in Settsu Province. Raishū returned to the Kinai to lead ikki forces against the Hosokawa army, but, in 1535, after Shōnyo and Harumoto reconciled, he was removed from his position for being an advocate of the war and withdrew from the Hongan Temple. In 1536, his younger brother, Shimotsuma Raisei, was assassinated in Sakai, while the lineage of his uncle, Shimotsuma Raikei (an advocate for peace), gained prominence as head priests of the Hongan Temple. In 1539, Raishū was killed in Ōmi by assassins sent by Shōnyo. The ouster and assassination were regarded as a means to hold Raishū responsible for triggering the Tenbun Disturbance.