Saitō Myōchin served as a bushō and priest from the Muromachi to early Sengoku periods.  Myōchin was his Buddhist name and his real name is uncertain.  Myōchin managed the Jizein sub-temple at the Zenne Temple so he was called Jizein-Myōchin.  Among the families affiliated with the Saitō clan, his lineage is referred to as the Jizein family.

In 1411, Myōchin was born as the son of Saitō Sōen, the deputy military governor of Mino.  He was the adoptive father of Saitō Myōjun.

In his youth, Myōchin entered the priesthood and, after undergoing training at the Zenne Temple, he managed the Jizein sub-temple.  In 1450, he invited Sesonin Nippan from the Myōkaku Temple and erected the Jōzai Temple.  Over a long period, Myōchin lived as a monk at Jizein.  In 1460, following the death his older brother, Saitō Toshinaga, he moved to Kanō Castle to serve as a guardian for his nephew, Saitō Toshifuji, who became the new deputy military governor of Mino.  In this location, he established a prayer hall and hermitage called Jizein.  While serving Toki Shigeyori, the military governor of Mino, he also attempted to act as a direct retainer of the Ashikaga shōgun family.  Myōchin had further aspirations to govern several provinces neighboring Mino.  Later, he became a member of the hōkōshū, a military organ under the direct jurisdiction of the shōgun of the Muromachi bakufu.  He was invested with the title of Junior Third Rank and Provisional High Clergy of the Second Rank, exceeding Shigeyori who carried the title of Junior Fifth Rank (Lower).

During the Ōnin-Bunmei War, Myōchin, together with Shigeyori, joined the Western Army led by Yamana Sōzen.  While Shigeyori was en route to Kyōto, Myōchin fought on his behalf against the Tomishima and Nagae clans affiliated with the Eastern Army, in addition to forces from the Kyōgoku clan who came to their support from Ōmi.  In the tenth month of 1468, he expelled them and pacified Mino.  After seizing many sōen, or manors, he amassed power surpassing his lords, the Toki clan.

In the summer of 1469, to support Rokkaku Takayori of the Western Army during an offensive in Ōmi, Myōchin attacked and defeated Kyōgoku Masatsune of the Eastern Army and Taga Takatada, the deputy military governor, in the second month of 1471 and, again, in the ninth month of 1472.

In the tenth month of 1473, Myōchin deployed to Ise Province in support of the Nagano clan and toppled Umedo Castle defended by the Eastern Army.  In the sixth month of 1474, he headed toward Echizen to mediate a dispute between Asakura Takakage and Kai Toshimitsu.  Around this time, generals in the Western Army attempted to settle, but were opposed by Myōchin.  After Myōchin departed on an expedition to Ise, Ogasawara Ienaga and Kiso Ietoyo took advantage of the opening to invade eastern Mino from Inadani and Kisodani.

The Tōyama clan of eastern Mino could not stop them, leading to the fall of Ōi Castle in the Ena District and Kariyasu Castle in the Toki District.  A portion of eastern Mino was occupied until the withdrawal of Ogasawara Sadamoto of Shinano in 1534.

After almost eleven years of conflict, as the Ōnin-Bunmei War drew to a close, a feeling of war-weariness pervaded the capital of Kyōto.  In the winter of 1477, Toki Shigeyori brought Ashikaga Yoshimi and Ashikaga Yoshiki (father and son) from Kyōto to Mino.  Yoshimi and Yoshiki resided at Kawate Castle in Mino.  The presence of nobles who fled the capital along with members of the Ashikaga clan enabled the culture of Kyōto to flourish in the town surrounding Kawate.  The decision for Shigeyori to accompany Yoshimi and Yoshiki to Mino at the end of the war was in accordance with the will of Myōchin.

In 1478, Myōchin joined forces with his son-in-law, Oda Toshihiro, and deployed to Owari Province, exercising his military capabilities outside of Mino.  He mediated the dispute between the Anekōji and Mitsuki clans of Hida Province and, according to Buddhist tradition, held a memorial service in Mino for the sixth shōgun, Ashikaga Yoshinori, to mark the thirty-second anniversary of his death.

In the second month of 1479, Myōchin retired to Akechi in the Kani District of Mino and, on 2/21 of Bunmei 12 (1480), died of illness.  He was buried at the Zuiryō Temple built in 1468.  In his will, he requested Shigeyori to rely upon Saitō Toshikuni, his adopted nephew (and younger brother of a different mother of Myōjun and Toshifuji).  As a result, within 100 days after his death, a sibling conflict broke out between Toshikuni and Toshifuji.

Character

Myōchin maintained friendly relations with leading cultural figures of his era, including Ichijō Kaneyoshi, Tō Tsuneyori, Sōgi, Banri Shūku, and Senjun.  In 1473, at the height of the Ōnin-Bunmei War, Myōchin invited Kaneyoshi to visit him in Mino to participate in a renga, or linked-verse poetry, event.  During the outbreak of the Ōnin-Bunmei War, Tō Tsuneyori, the lord of Shinowaki Castle in Mino, was residing in Shimōsa Province while his older brother, Tō Ujikazu remained in Mino.  Based on suspicions that Ujikazu was colluding with the Tomishima clan, Myōchin attacked and caused him to flee, whereupon Myōchin occupied his territory.  Tsuneyori wrote a poem lamenting the take-over which was communicated as hearsay to Myōchin.  Myōchin then said that if Tsuneyori sent a poem directly to him, he would return the land.  Later, after the two exchanged poems, Myōchin followed through on his offer.  During the Ōnin-Bunmei War, Sōgi also frequently traveled to Mino and hosted renga events.

Myōchin was skilled in political and military affairs, and wielded economic power as well.  An official named Mibu Haretomi praised him as a person of unparalleled integrity and authority; another individual named Ōmiya Nagaoki referred to him as resourceful in battle, and another account said that the fortunes of those across the land depended upon the advance or retreat of Jizein.

Many accounts treat Myōchin as the same individual as Saitō Toshifuji.  One account, however, proposes that he may have been the younger brother of Saitō Toshinaga.  According to other accounts, he was Toshifuji’s uncle (the younger brother of Toshinaga).  Alternatively, Myōchin was the younger brother of Toshinaga and the same person as Zenneji.  Accordingly, Toshifuji, and not Myōchin, succeeded Toshinaga as the deputy military governor of Mino.