Kojiki is the earliest historical record in Japanese history. This book is firstly used to record inheritance and restore the nature of history with exact details.
In ancient Japan, some diplomats were sent to Tang dynasty and brought knowledge from China. The books were written by Chinese characters and, based on the Chinese characters, Manyogana was created. Manyogana is used to write kana in Chinese. But the grammar is same as kana. When Chinese character was introduced to Japan, kana was not formed yet. Thus, Japanese chose tens of Chinese characters to mark the pronunciation. That is Manyogana. Since then, they simplified the Manyogana in order to separate Chinese characters and their words. Thus, Manyogana was also assumed as the rudiment of hiragana and katagana
However, the Manyogana was too prolix and Chinese characters were too complex to explain the main ideas. Hence, the author chose to mark with phonetic symbols to explain the words. Besides, the author explained the verbs and auxiliary rigorously. But Nohongi was completely written by Chinese characters. Thus, this is the largest difference between Nihongi and Kojiki.
Comparing with Nihongi, Kojiki was written in ancient Japanese instead of Chinese characters. Thus, it is an important example for historians to research the ancient Japanese. However, because of the limitations of the grammar and structure, some contents in Kojiki was not clear and coherent and even, loss of some necessary verbs and auxiliary. That was the deficiency of Kojiki comparing other ancient historical records.
(Shinpukuji-bon Kojiki)
Reference:
https://en.wikipedia.org/wiki/Kojiki
Philippi, Donald L, translator. Kojiki. Princeton University Press, 1969.
Brownlee, John S. Political Thought in Japanese Historical Writing: From Kojiki (712) to Tokushi Yoron (1712). Wilfrid Laurier University Press, 2006, pp. 14-41.
