As something that shows the condition in which the East Asian classics truly existed in Japan, the way that they adjusted Buddhism, which is one half of the East Asian classics along with the Chinese canon, I first recommend Kūkai’s Sangō shiki (available from Iwanami shoten, Nihon koten bungaku zenshū, Chikuma shobō, Kōbō daishi kūkai zenshū, etc.). As stated in the title, the three teachings of Buddhism, Confucianism, and Daoism are contrasted and spoken upon by an invented fictional character who in the end explains the superiority of Buddhism. We can plainly see here how the East Asian classics, which cover Buddhism, Confucianism, and Daoism, were read, used, and the manner in which new literary products were created during the mid-eighth to early ninth century when Kūkai lived. More importantly, Sangō shiki continued to be read in later periods, and coupled with other enlightening contents, served as a handbook for study of the East Asian classics. Particularly in the early modern period, many copies of the commentaries Sangō shiki kanchū and Sango shiki sanpo were published, and while they take the position of explicating Sango shiki, these works also opened the door to the classics for a wider audience of readers.
The beginning of the preface of Sangō shiki the phrase “rinka (鱗卦), danpen (聃篇), shūshi (周詩), sofu (楚賦)” appears. Rinka refers to the Book of Changes, Danpen to the Laozi, shūshi to the Book of Songs, and sofu to the Songs of Chu. From the Confucian classics and other texts outside that tradition, works that represent both prose and poetry are combined, and Kūkai’s education in the classics is illustrated by expressions taken from the continental canon. Concerning the Songs of Chu, I suggests Kominami Ichirō’s Songs of Chu (Chikuma shobō, Chūgoku shi bun sen). This is an entry level book that fascinatingly explicates the difficult poetic verse of the Songs of Chu, taking as its background the ancient culture of Southern China, which differs from that of the North China Plain.

Japan’s first collection of Buddhist setsuwa Nihon ryōiki was compiled in the same era as Sangō shiki. The existence of Buddhist setsuwa is not limited to the Buddhist canon, and the method for explaining and telling local realities was already seen in China, as evinced by Makita Tairyō’s Rikuchō koitsu kanzeon ōkenki no kenykū (Hei rakuji shoten, 1970).

For an introduction to Kūkai as a person, I recommend Takeuchi Nobuo’s Kūkai nyūmon: kōnin no modanisuto (Chikuma shinsho, 1997). It reads the poetry left behind by Kūkai, but teaches the interesting issues in study of the classics by bringing us closer to the time and space in which Kūkai lived. For learning the classics in relation to Kūkai, and in particular the importance of Siddham research, it is good to also read “Kūkai to shittan” (Hikaku bungaku kenkȳu 56, 1989) by the same author.

For a work that represents the study of the East Asian classics in the medieval period, I suggest Ichijō Kaneyoshi’s Nihon shoki sanso (Yagi shoten, Tenri toshokan zenbon sōsho, Shintō taikei hensankai, Shintō taikei Nihon shoki chūshaku 2). This is a commentary on the divine-age volumes of Nihon shoki, but as it is based on the conviction that mythology as told in the Nihon shoki matches the teachings of Buddhism, Confucianism, and Daoism, the explication uses citations from the Chinese and Buddhist canons. Interestingly, these citations do not always follow the original sources verbatim, instead relying on encyclopedias and digests such as Taiping yulan and Shiwen leiju from the Chinese canon and Zong jing lu, Fo zu li dai tong zai, Fan yi ming yi ji from the Buddhist canon. Also, use of dictionaries like Gu jin yun hui ju yao and a variety of commentaries from the neo-Confucian and Zen traditions allows a glimpse of the state of an episteme in the medieval period. Many points on how Sanso uses the classics are still buried, and excavating them is an ingenious way to learn the concrete and living form of the classics in Japan.

Concerning the horizon of the medieval (secret religious transmission could also be said) episteme that Kaneyoshi confronted in his time, in recent years vigorous study is progressing. Among these studies, the classics are already represented as achieving a radical transformation. Results from this approach are Ise Satoru’s Chūsei tenshō daijin shinkō no kenkyū (Hōzōkan, 2011), Abe Yasurō’s Chūsei nihon no shūkyō tekisuto taikei (Nagoya University Press, 2013), Ogawa Toyoo’s Chūsei nihon no shinwa moji shintai (Shinwasha, 2014), and others.

Finally, for me, the interestingness of facing the classics and their lived form comes from directly experiencing concrete texts, manuscript and printed., Yamamoto Nobuyoshi’s Kotenseki ga kataru: shomotsu no bunkashi conveys this fascination with the classics as objects, as told by a master of research on these texts.