Chusei Nihongi (A set of medieval Japanese myths) (中世日本紀)
Chusei Nihongi collectively refers to a set of Japanese mythologies that were variously reinterpreted and revised based mainly on the Honchi Suijaku theory (the theory that Japanese deities were the multi-faceted embodiment of Buddha) in the medieval period while founding its base on classics such as "Nihonshoki" (Chronicles of Japan). It is also an academic term that refers to the above-mentioned reinterpretation and revision movement. The former is also called 'Chuse Shinwa' (Medieval Japanese Myths).
In Chusei Nihongi, it is often the case that Shinto deities described in the Kojiki (Records of Ancient Matters) and the Nihonshoki are identified with Buddhist devas and many types of celestial Buddhas. Chusei Nihongi features myths built on "Shjnbutsu Shugo Shiso" (syncretism of Shinto and Buddhism), which prevailed in medieval Japan, such as Ryobu Shinto (a fusion of Shinto and the Shingon sect of Buddhism) and Sanno Shinto (a fusion of Shinto and the Tendai sect of Buddhism), whereby Shinto deities and Buddhist gods play on a level playing field. Also, even in cases where Shinto deities are not identified with Buddhist devas or celestial Buddha, the influence of Buddhism can be observed in the interpretation of mythologies. There are no integrated and systematized documents about Chusei Nihongi because they are described in many books about the study of waka poems, war chronicles, histories of temples and shrines etc., but the plentiful variety of Chusei Nihongi are preserved.
Background
In the medieval period, Buddhism permeated all levels of society and sought abstract but rational logic, although occultism remained. During the period of the Ritsuryo system (a system of centralized government based on the ritsuryo code), the interpretation of "Nihonshoki" had been done mainly by ranked officers, professors of the Bureau of Education, and clans in charge of religious ritual services, who handled ceremonies in the Imperial Court. Under the system of the dynasty state, however, the interpreters of Nihonshoki gradually shifted to Esoteric Buddhist monks, pundits of waka poem studies, and the jinin (associates of Shinto shrines) of each shrine, and initiatives to reinterpret mythologies based on Buddhist philosophy started.
For example, Esoteric Buddhism-related books, such as "Story of Mt. Koya," explain that the Ama-no-iwato myth (Shinto goddess of the Sun hid behind the Cave of Heaven but was enticed out by many deities) depicts the following process: the gate of the iron pagoda in Nantenjiku (South India) opens thanks to the merciful glow of Vairocana Buddha (metaphor of achieving enlightenment) when the enlightenment of all creatures was covered by the long night of earthly desires. Also, this period saw the emergence of books where episodes not cited in the original of Chronicles of Japan are introduced as ones quoted in the Chronicles of Japan; an example of such books is "Kokin Wakashu Jomonsho Sanryu-sho" (Excerpts from "A Collection of Ancient and Modern Japanese Poetry "and Explanatory Notes), which reads that "The Tale of Bamboo Cutter is cited in the Chronicles of Japan."
Worship of Ebisu (Japanese god of luck)
According to "Taiheiki" (The Record of the Great Peace), Hiruko (a deity in Japanese mythology) can be identified with Nishimiya Daimyojin (Shinto-Buddhism great human god of Nishimiya-jinja Shrine). It is said that this theory was narrated by Kanekazu URABE of the Urabe family, a family that had made a profession out of interpreting the "Chronicles of Japan" for generations. Also, books such as "Heike Monogatari" (Tale of the Heike), "Genpei Seisui-ki" (Rise and Fall of the Minamoto and the Taira clans), "Kokin Wakashu Jomonsho Sanryu-sho," and "Shintoshu" (Buddhist Rendition of Shinto Myths) introduce the belief that "Hiruko can be identified with Ebisu (Japanese deity of prosperity) "from a wider perspective: "Hiruko was washed up on Settsu Province and became 'Ebisu-Saburo dono'."and "Nishimiya (shrine) was given to Hiruko by Amaterasu Omikami (the Sun Goddess)."
Ama no Murakumo no Tsurugi Sword
In the "Chronicles of Japan" (in the Record of Emperor Tenchi), there is an episode about Dogyo, a monk from Silla, trying to steal the Ama no Murakumo no Tsurugi Sword, a sacred sword (one of the Three Sacred Treasures of Japan) of Atsuta-jingu Shrine, from the shrine and bring it back to Silla. In the "Record of Hakozakigu Shrine" by OE no Masafusa, however, this story is introduced differently: when Ama no Murakumo no Tsurugi Sword, which made many failed attempts to escape from Dogyo, is finally cornered, Hachimanshin (Shinto god of war), the locally-adjusted form of Amida Buddha, kicks Dogyo to death and seizes back Kusanagi no tsurugi (another name of Ama no Murakumo no Tsurugi Sword). A similar version is also found in the "Tale of the Heike," whereby Atsuta Myojin (Shinto-Buddhist human god of Atsuta-jingu Shrine) orders Sumiyoshi Daimoyojin (Shinto-Buddhism great human god of Sumiyoshi-jinja Shrine) to chase Dogyo and kick him to death.
Also, books such as "Tale of the Heike," "Gukansho" (Jottings of a Fool) record that Emperor Antoku (a child emperor of Heike origin who was drowned at sea with the Ama no Murakumo no Tsurugi Sword as a result of the defeat of the Heike clan) is the reincarnation of Yamatanoorochi (eight-headed and eight-tailed dragon), and that Yamatanoorochi took back his stolen treasure sword (Ama no Murakumo no Tsurugi Sword is said to be effectuated from the tail of Yamatanoorochi) and brought it back to Ryugu (the Palace of the Dragon King in the deep sea). With this, the "Record of the Great Peace" explains that the reason why the Imperial family saw the decline of their power after the Jokyu War and the rise of the warrior class is that the sacred sword sank in the deep sea, and continues that the Sun goddess had the sacred sword washed up on the coast of Ise by providing her decree to Ryugu.
Dairokuten Mao and Amaterasu Omikami
In the "Shasekishu" (collection of Buddhist stories), the following episode is introduced as a tale heard from a Shinto priest of Ise-jingu Shrine.
When creating the nation of Japan, Amaterasu Omikami discovered the impression of the seal of Vairocana Buddha in the sea and rummaged through the seabed for the impression with her sword.
A drop fell from the sword at this time. Observing the scene, Dairokuten Mao (an evil spirit who prevents people from becoming Buddha) tries to destroy the nation, saying "I can foresee that this drop will become a nation, where Buddhism will spread, and the birth and death of humans will continue."
Amaterasu Omikami turns Mao away, snapping, "I won't chant the name of Sanpo (3 treasures of Buddhism: Buddha, sutras and priesthood) and allow them to come closer to me. So go home!"
To keep this promise, Ise-jingu Shrine prohibits Buddhist monks from visiting the shrine and requests followers to use metaphors when uttering Buddhist words, but followers remain sincerely true to Sanpo stealthily deep in their heart in reality.
Similar episodes are also found in books such as "Tale of the Heike" and "Record of the Great Peace:" in exchange for Amaterasu's promise, Dairokuten Mao gave her Yasakani no magatama (comma-shaped jewel, one of the Three Imperial Regalias - in medieval Japan, Yasakani no magatama was considered to be a seal). Incidentally, "Tsukai Sankei-ki" (Records of Buddhist Monk Tukai's Pilgrimage) reads that it was Izanagi and Izanami who made a promise to Dairokuten Mao.
It is pointed out that this episode formed the foundation to the exclusion of Amaterasu Omikami from kishomon (sworn oath) for a certain period in the Kanto areas because "She is the goddess who tells a lie."
Toyouke no Okami (Grand Divine Toyouke)
In the Ise Shinto, the Watarai clan, household in charge of priesthood for Ise-Geku (outer shrine of Ise-jingu Shrine) - trying to upgrade Toyoukebime, a deity enshrined in Geku, as a deity either equaling or surpassing the one enshrined in Naiku (inner shrine/enshrined deity: Amaterasu Omikami) - identified Toyoukebime with Ame no Minakanushi no Kami and Kunitokotachi no Kami, deities who had appeared prior to tenchikaibyaku (creation of heaven and earth in Japanese mythology), and created a variety of legends to endow Toyoukebime with universal divinity surpassing Amaterasu Omikami. Ise Shinto itself was built on the Shinponbutsujaku theory (Buddhist devas and types of Buddha are other forms of Shinto deities), antithesis of the Honji-suijaku theory (Shinto gods are locally-adjusted forms of Buddhism devas and types of Buddha). However, it is pointed out that the theory of "Shinto Gobusho" (five-volume apologia of Shinto), the foundational book of the Ise Shinto, is influenced by "Yamatokatsuragihozan-ki," a book that discusses Shintoism from a Buddhist perspective, particularly Shugendo (Japanese mountain asceticism-shamanism incorporating Shinto and Buddhist concepts).
Also, based on the fact that a magnificent shrine such as Geku was constructed for a culinary deity (Toyoukebime is a culinary deity) in the first place, there is a belief that this is, literally, an initiative for the resurrection of Toyouke Daijin (Shinto-Buddhism version of Toyoukebime). Toyouke Daijin was an important deity for the Imperial family, but there was also a possibility that it was a dangerous deity who may endanger the uniquely sacred position of the Imperial family, for example due to the emergence of powerful clans who worshipped Toyouke Daijin.
Later Stage
Since the release of "Kojiki-den" (Commentary on the Kojiki) authored by Norinaga MOTOORI, trends in the interpretation of Japanese mythology went to the direction of excluding "karagogoro" (Chinese influence), such as Confucianism and Buddhism, and paved the way for the birth of State Shinto in early modern times. In particular, due to the separation of Buddhism and Shintoism, which was promoted during the Meiji Restoration, the synthesis of Shinto and Buddhism suffered a fatal blow and was excluded from the center of Shinto teachings, which, under Jinjahishukyoron (theory that Shinto is not a religion), shed religious colors and figured on becoming practical, ritualistic, and spiritual pillars for the people. Chusei Shinwa, meanwhile, was discarded as implausible superstition and scarcely paid heed to throughout the early modern times. Recently, however, research on Chusei Nihongi has progressed in the fields of mythology and history, in addition to traditional study from the viewpoint of Japanese literature. In the field of literature, Chuse Nihongi has been redefined as an ideological experiment that figured on the establishment of high-level metaphysics equal to Buddhism based on the existing system of Japanese mythologies. In the field of history, Chusei Nihongi is reevaluated as a good approach for the system of the dynasty state to reorganize the spiritual world of the warrior class and others, who acquired Buddhist-like rationalism.