Shimotsuma Raisei served as a bushō during the Sengoku period. He was a bōkan, or head of administrative affairs, at the Hongan Temple.
Together with his older brother, Shimotsuma Raishū, Raisei established relations with Shōnyo, the tenth abbot of the Hongan Temple and Shōnyo’s guardian and maternal grandfather, Renjun. Shōnyo’s succession to this role occurred in 1525 after the death of his paternal grandfather, Jitsunyo, who served as the ninth abbot of the Hongan Temple. Shōnyo’s father, Enyo, earlier died in 1521, making Shōnyo the lineal successor.
In 1531, a conflict arose in in the Hongan Temple (whose members were adherents of the Jōdo-Shinshū sect) in Kaga in regard to reformation of the religious group. This event was known as the Kyōroku Disturbance or, alternatively, as the Dai-shō 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.
During the Dai-shō ikki, Raisei assisted Jikken, the fifth abbot of the Chōshō Temple and son-in-law of Renjun. Jikken was affiliated with the Dai-ikki. With the support of the Shimotsuma and monks from the Kinai and Tōkai regions who deployed upon orders of Rene and Renjun of the Hongaku Temple, Jikken fought against and defeated the Shō ikki and Rengo of the Honsen Temple as well as additional forces led by Asakura Norikage (Sōteki) and Hatakeyama Ietoshi. Those supporting the Shō-ikki were forced into exile, after which Jikken was on a par with the Hongaku Temple as a member of the governing class in Kaga.
From 1532 to 1535, the Tenbun Disturbance was marked by conflict between the Hongan Temple against the Hosokawa and Hatakeyama clans. During this period, Raisei returned to Kinai and, while leading ikki forces, engaged in battles in Kawachi and Settsu provinces. In 1535, after Shōnyo and Hosokawa Harumoto reconciled, Raisei, as a member of the warring faction, was demoted. Raisei and Raishū then departed from the Hongan Temple.
The Kyōroku Disturbance and the Tenbun Disturbance, having occurred as sequential events, are referred to together as the Kyōroku-Tenbun Conflict.
In 1536, Raisei participated as a unit commander of ikki forces at Nakajima Castle in Settsu but was defeated by Kizawa Nagamasa and fled. Later, Raisei he was killed in the bustling harbor town of Sakai by an assassin sent by Shōnyo. Further, in 1539, Raishū was killed in Ōmi Province, also by assassins sent by Shōnyo.