The Nihon Shoki (日本書紀?), sometimes translated as The Chronicles of Japan, is the second oldest book of classical Japanese history. The book is also called the Nihongi (日本紀, lit. Japanese Chronicles?). It is more elaborate and detailed than the Kojiki, the oldest, and has proven to be an important tool for historians and archaeologists as it includes the most complete extant historical record of ancient Japan. The Nihon Shoki was finished in 720 under the editorial supervision of Prince Toneri and with the assistance of Ō no Yasumaro.
The Nihon Shoki begins with the Japanese creation myth, explaining the origin of the world and the first seven generations of divine beings (starting with Kunitokotachi), and goes on with a number of myths as does the Kojiki, but continues its account through to events of the 8th century. It is believed to record accurately the latter reigns of Emperor Tenji, Emperor Temmu and Empress Jitō. The Nihon Shoki focuses on the merits of the virtuous rulers as well as the errors of the bad rulers. It describes episodes from mythological eras and diplomatic contacts with other countries. The Nihon Shoki was written in classical Chinese, as was common for official documents at that time. The Kojiki, on the other hand, is written in a combination of Chinese and phonetic transcription of Japanese (primarily for names and songs). The Nihon Shoki also contains numerous transliteration notes telling the reader how words were pronounced in Japanese. Collectively, the stories in this book and the Kojiki are referred to as the Kiki stories.
The tale of Urashima Tarō is developed from the brief mention in Nihon Shoki (Emperor Yuryaku Year 22) that a certain child of Urashima visited Horaisan and saw wonders. The later tale has plainly incorporated elements from the famous anecdote of "Luck of the Sea and Luck of the Mountains" (Hoderi and Hoori) found in Nihon Shoki. The later developed Urashima tale contains the Rip van Winkle motif, so some may consider it an early example of fictional time travel.
Read more about Nihon Shoki: Chapters, Process of Compilation, Exaggeration of Reign Lengths