Mikkyo, Esoteric Buddhism (密教)
Mikkyo is an abbreviation for Himitsu Bukkyo, or esoteric Buddhism. Among Mikkyo believers it is also called Vajrayana, as opposed to Mahayana Buddhism and Hinayana. It identifies itself as Buddhism, but among scholars there is controversy as to whether Mikkyo is included in Buddhism or not.
While in Mahayana Buddhism (exoteric Buddhism) dharma is preached broadly to people through words and texts, characteristically in Mikkyo a very mystical and symbolic dharma is transmitted by a master to a disciple within the sect.
The reason that Tibetan Buddhism, which took over Indian Mikkyo, was previously called 'Lamaism' is due to the characteristic that a disciple believes his 'lama' absolutely at the time of transmittal.
The ritual by which to prove that a master has completely transmitted dharma to a disciple is called Denpo Kanjo (伝法灌頂), and the complete transmission of dharma is compared to 'pouring water from a bottle to another bottle without spilling a drop.'
The course of Mikkyo's establishment
In the background of Mikkyo's establishment was such a social situation that Buddhism was oppressed as Hinduism flourished during the latter period of Indian Buddhism. Mikkyo tried to revive Indian Buddhism by incorporating the elements of Hinduism into Buddhism. However, the incorporation of Mikkyo with Indian Buddhism could not limit the growth of Hinduism, and as a result Indian Buddhism declined. Soon, it was attacked politically and diplomatically from two sides: one, by the Islamic government (Delhi sultanate) that had invaded from northern India, which was ruled by Muslims from Western Asia; and secondly, by the Hindu government of southern India. Attacked by Islam for its worship of an idol and magical elements, Mikkyo in India was forced to disappear into history as the last stage of Indian Buddhism.
The early stage of Mikkyo
The early stage of Mikkyo, Zo-mitsu (the Mixed Esoteric Buddhism), which was established at the stage when magical elements were incorporated into Buddhism, was not particularly systematized but aimed to gain practical benefits in this world by reciting mantra, Shingon and litany, as well as the spell of each Buddha, being affected by the mantra of Brahmanism, in which religious services were performed. There was no Mikkyo sutra, and a curse on (咒) and litany were seen in the various sutras of Mahayana Buddhism.
The middle stage of Mikkyo
In order to protect against the emergent Hinduism, the middle stage of Mikkyo was established more seriously as a systematized form of Buddhism. The middle stage of Mikkyo, as opposed to the Mahayana Buddhism in which a form of Shakamuni was preached, compiled Mikkyo sutras consisting of the teachings of 大毘盧遮那仏（Mahāvairocana), or Dainichinyorai by another name. After the accomplishment of "Dainichi-kyo Sutra," "初会金剛頂経"（Sarvatathāgatatattvasaṃgraha） and their commentary, Mandala, which showed the world view of Mikkyo incorporating various Buddhas, was produced; thus the Buddhas of Mikkyo were placed into a hierarchyand systematized, as all Buddhas were created from Issainyorai (一切如来), the Five Buddhas of Wisdom around Dainichinyorai: Gochinyorai (五智如来).
While the middle stage of Mikkyo became a complicated system of Buddhism for priests, it couldn't become widespread among Indian people and therefore couldn't change the trend whereby Hinduism, which emphasized daily religious services and folk beliefs, flourished and expanded. For this reason, in order to hold out against the flourishing of Hinduism in India, there appeared Funnuson (憤怒尊) and Gohoson (護法尊) to pray for the protection of the training of Buddhism and the surrender of the enemy, such as Gozanze Myoo, who defeated Shiva, and Mahakala, who subdued Ganesha and Gundari Myoo.
The late stage of Mikkyo
Because the middle stage of Mikkyo couldn't hold out against the flourishing of Hinduism, the late-stage of Mikkyo, which valued practice instead of theory, was established. In the late stage of Mikkyo, the principle of Buddha's nature was pursued. Accompanied by this, Hosshin Fugen (法身普賢), Gonkosatta and Kongo Soji (金剛総持) became to be respected as 最勝本初仏 mostly.
Additionally, being influenced by the tantora of Shakta Hinduism and Shakti belief, Anunttara-yoga was seen characteristically in the late-stage Mikkyo, which was a training of coalescence (sex) between male principles (mind, wisdom, upaya and Vajradhatu) and female principles (body, feeling, Hannya and Garbhadhatu), so that there appeared joyful Buddha (歓喜仏) which showed that the male Buddha (male principle) and female Buddha (female principle) had sexual intercourse. In the development of research on yoga tantra, bringing Purana to the top of the head from the lower body was regarded as the best way, and having sexual intercourse was considered the most efficient way for that. However, because of the ruined morals such as with male priests forcing lay female believers to have sexual intercourse as the best means of devoting their bodies, which they practiced despite the broken precepts, some Buddhists left the late-stage Mikkyo and returned to Theravada Buddhism, which valued the religious precepts. As a response to criticism against priests' having sexual intercourse, the content of Anunttara-yoga was changed from a practice of having sexual intercourse to one in which intercourse was imagined.
Additionally, since Indian Buddhism was expected to collapse under the Muslim invasion in the political and social situation at that time, the Kala cakra tantra (the last Mikkyo sutra) described the following: the flourishing of Islam; the collapse of Indian Buddhism, a concept of Shambhala; a secret Buddhist land and Utopia, which could be reached only through Mikkyo during the period before the revival of Indian Buddhism (the Age of Final Dharma); Raja Cakravarti (ルドラ・チャクリン（転輪聖王）), who became the thirty-second king of Shambhala; a counterattack by Raja Cakravarti against the invaders (Muslims); the prediction that Raja Cakravarti would destroy the king of evil and his supporters in the final war; the revival of Indian Buddhism in the future; the return to order on earth; the coming of the harmonization and peace of the world, and so on.
The Muslim invasion and destruction in northern India interrupted Buddhism (including Mikkyo in India), but a developed system of late-stage Mikkyo can be seen in Tibetan Buddhism.
Mikkyo in Japan
In Japan, Mikkyo was first introduced by Saicho (Dengyo Daishi), who had returned from Tang. The Imperial Family and aristocrats at that time were interested in Mikkyo, which valued practical benefits in this world or "pure land" teachings, as well as Jodo-kyo (Buddhist invocation), which promised reincarnation in the Land-of-Bliss/Pure Land of the next world, instead of the Tendai Doctrine, which Saicho had seriously studied. However, because Saicho mainly studied the Tendai Doctrine but did not do so with Mikkyo, Mikkyo was introduced more properly by Kukai (Kobo-daishi), who studied it at Shoryuji Temple, Qinglongsi Temple (the basis of Chinese Mikkyo), Engyo, Ennin (Jikaku Daishi), Eun, Enchin (Chisho Daishi) and Shuei.
Among the traditional Buddhist sects in Japan, the Shingon sect (whose teachings Kukai learned from Eka) and the Keika of Shoryuji Temple (Xian City) in China (Tang), thus systematized as Shingon Mikkyo (Toumitsu; Shokushin Jobutsu and the guard of the nation being two aspects), and the Nihon Tendai sect (called Daimitsu in some cases), which was begun by Saicho and established by Ennin, Enchin and Annen, are incorporated into Mikkyo. While members of the Shingon sect learn Mikkyo independently, members of the Tendai sect learn Tendai, Mikkyo, Buddhist precepts and Zen at the same time. Tomitsu means the Mikkyo of To-ji Temple (Kyoogokoku-ji Temple), and Daimitsu means Tendai Mikkyo.
While Tomitsu and Daimitsu, which were transmitted systematically, are called Jun-mitsu (Pure Esoteric Buddhism), Mikkyo, which had been transmitted in fragments and had adherents before Jun-mitsu, is called Zo-mitsu (Mixed Esoteric Buddhism).
Mikkyo in China
In modern China, Chinese Mikkyo, which flourished in the Tang Dynasty (the middle-stage Mikkyo) is called 唐密宗 and Mikkyo in Tibetan Buddhism continues to be called 西蔵密宗. Mikkyo, which Kukai, Ennin and Enchin of Japan learned in Tang, was 唐密宗. 唐密宗 declined and was interrupted due to the oppression of Zen and Buddhist invocation (pure-land teachings, Jodo-kyo) after the Tang Dynasty. In modern China, an effort is being made to revive 唐密宗 through an exchange with the Shingon sect of Japan (Tomitsu) such as Seian-ji Temple in Shanghai, but it is a minor activity. 西蔵密宗 has been believed until now around the autonomous region of Tibet and northern China.
It is considered that the reason that 唐密宗, the middle-stage Mikkyo, declined and was interrupted is that Taoism--which was a rival having the same aspects of practical benefits in this world, as well as mojo--was favored. It is said that Confucianism also had a strong influence in China, so that the late-stage Mikkyo, which flourished in Tibet, Nepal and Mongolia, was not introduced because tantra was in opposition to sexual morality.
A hypothesis on Indian alchemy
Moreover, there is a hypothesis that Indian alchemy became Mikkyo and that Mikkyo was alchemy itself, but it is not widely accepted and remains untried in Buddhist studies.
By extension, the religion and sects that have mystical and symbolic dharma, such as cabala, kabbalah and Booduism, other than Buddhism, are in some cases referred to as Mikkyo. It is also called Mitsugi Shukyo (密儀宗教).