Ryōyū 良祐 (active mid- to late-12th century, traditional lifedates 1107–1190) was a late-Heian to early-Kamakura Tendai esoteric (Taimitsu 台密) master, founder of the Sanmai-ryū 三昧流 (Samādhi-lineage) sub-line within the broader Kawa-ryū tradition. He was a successor of Chōen 長宴 (長宴) and his lineage produced major medieval Taimitsu procedural compendia.
His KR6t0111 Sān-mèi liú kǒu-chuán jí 三昧流口傳集 (“Collected Oral Transmissions of the Sanmai-ryū”) is a two-fascicle compendium of the Sanmai-ryū kuden corpus, covering rites for shén-gōng 神供 (deity-offerings), sì-zhǒng màn-tú-luó 四種曼荼羅 (the four maṇḍala types), sān-zhǒng xī-dì 三種悉地 (the three siddhis), zūn-shèng 尊勝 (Uṣṇīṣa-vijayā) rites, and the Zūn-shèng vajra-pāramitā contemplation. Like other Tendai-esoteric kuden compendia, the work preserves the procedural and doctrinal-interpretive material that defined his sub-lineage’s identity within Hiei-zan Taimitsu.
His lifedates are uncertainly attested; the compilation of his kuden-shū is conventionally placed in the late twelfth century.