The moment
Two monks who sailed to Tang China in 804 came home with new schools. Saichō returned in 805 to build Tendai on Mount Hiei, whose monastery became the training ground for most of Japan's later founders; Kūkai returned in 806 with the esoteric teachings of his master Huiguo and established Shingon. The two schools dominated Japanese Buddhism for centuries.
People: Saichō, Kūkai