Shinsei 眞盛 (1443–1495), posthumous titles Enkai Kokushi 圓戒國師 (“National Master of the Perfect Precepts”) and Jishō Daishi 慈攝大師, was the founder of the Tendai Shinsei-shū 天台真盛宗 — one of the three principal medieval-to-early-modern Tendai branch schools, alongside the Sanmon and Jimon sub-schools. He was a successor in the Kurodani 黑谷 / Ninkū (仁空) precept-revival lineage and the founder-restorer of the Saikyō-ji 西教寺 at Sakamoto, on the slopes of Mt. Hiei facing Lake Biwa.
Born in Ise Province, Shinsei entered Mt. Hiei as a youth and studied under the Kurodani precept-revival masters in the line of descent from Ninkū. He undertook intensive ascetic training including a twenty-year mountain retreat (according to the hagiographical tradition), and in 1486 established his teaching headquarters at the Saikyō-ji at Sakamoto, restoring this ancient temple as the principal seat of his synthesis of Tendai Bodhisattva-precept discipline with continuous nenbutsu recitation (the fudan-nenbutsu 不斷念佛 tradition).
His doctrinal program — the integration of Tendai enkai 圓戒 (Perfect-Precept) discipline with continuous-recitation nenbutsu practice — represents the final Tendai institutional response to the Kamakura-period Pure-Land-school separation. Where Hōnen (源空) and his successors had separated nenbutsu practice from Tendai discipline, Shinsei reintegrated the two — preserving the Tendai institutional and doctrinal framework while making continuous-recitation nenbutsu its central devotional discipline.
His writings include the KR6t0120 Zòujìn fǎyǔ 奏進法語 (“Dharma-Discourse Presented to the Emperor”) and KR6t0121 Niànfó sānmèi fǎyǔ 念佛三昧法語 (“Dharma-Discourse on the Nenbutsu-Samādhi”). His three principal disciples — Shinchō 眞迢, Shinka 眞荷, and Shinrō 眞朗 — produced the fǎyǔ (Dharma-discourses) collected at KR6t0122–KR6t0124.
Shinsei was canonized Enkai Kokushi in 1788 and Jishō Daishi in 1942. The Saikyō-ji remains the head temple of the Tendai Shinsei-shū sub-school.