Shingon Buddhism is a sect of esoteric Buddhism based on the teachings of Vajrayana. The word "Shingon" is the Japanese reading of Chinese Zhenyán (True Words), which in turn is the Chinese translation of the Sanskrit word "mantra." Shingon Buddhist doctrine arose during the Heian period (794-1185) after a Buddhist monk named Kukai traveled to China to study Vajrayana practices in the city of Xi'an under Huiguo, a favorite student of the legendary Amoghavajra. Shingon followers usually refer to Kukai as Kobo-Daishi. Central to Shingon is meditation on two mandalas, the vajradhatu (thunderbolt realm) mandala or Kongo Kai [More on Kongo Kai] and the garbhadhatu (womb realm) mandala or Taizo Kai [More on Taizo Kai].
The Kongo Kai or Mandala of the Diamond Realm is the other mystic diagram in the esoteric Buddhist system called the Mandalas of the Two Realms. These mandalas are used in meditation and in a variety of rituals, including initiation rituals in which the aspirant is blindfolded and asked to fling a flower on the mandala. The deity it lands on decides the central practice. The diamond mandala or male transcendental idea of the cosmos is based on the Vajrasekhara Sutra and embodies the aspect of Knowledge. It is made of up nine mandalas embodying various realms of reality, each presided over by an organization of Buddhas.
The Taizo Kai or Mandala of the Womb Realm is one of two associated mystic diagrams followed by esoteric Buddhism (Shingon, Vajrayana). These mandalas embody a transcendental organization of the cosmos and are used for meditation leading to cosmic experience. The womb realm or feminine matrix of the cosmos is based on the Mahavairochana Tantra and embodies the aspect of Compassion. At its center is the Transcendental Buddha beyond space and time, surrounded by four main and four subsidiary directional Buddhas. These are surrounded by concentric zones of phenomenal existence presided over by specific emanations of the Buddha.