Saicho, the founder of Japanese Tendai, initially placed himself as a student under Kukai, receiving esoteric initiations from him around 812, at a point when Kukai possessed transmission lineages and texts Saicho's own trip to China had not brought back. The relationship broke down within a few years, worn down by a request Kukai refused, Saicho asking to borrow a text rather than travel to receive it properly, and by the departure of Saicho's own disciple Taihan to study under Kukai instead. What survived the personal falling out was a doctrinal disagreement Saicho had already staked out: where Kukai held that the esoteric teaching surpassed the exoteric outright, superior in kind and not just useful alongside it, Saicho insisted the two belonged together inside a single Tendai curriculum, neither one demoted to a supporting role. The specific text at issue sharpens the disagreement rather than being incidental to it: Saicho had asked to borrow a commentary on esoteric ritual practice, and Kukai's refusal came with an explanation, that such teachings could not be transmitted by reading alone and required the direct relationship of initiation, itself already an assertion of exactly the ranking Saicho rejected, that esoteric transmission worked by a different and higher rule than ordinary scholarly borrowing. Paul Groner's study of Saicho's founding of the school describes this refusal to rank the two teachings as a deliberate structural choice reflected in Tendai training, which unlike Shingon required its monks to master both traditions of practice rather than specializing in the esoteric alone.