The indigenous religion of Japan is Shinto (神道), the "Way of the Gods". The central text of Shinto is the Kojiki (古事記), which outlines the ancient mythology whereby Japan's ancestral gods and lands were born. If you've ever taken a course in World Religions, you know how crucial myths are to any culture. Core myths explain why we do what we do; why we live like we live. For example, the Judaeo-Christian Creation story explains such things as why humans differ qualitatively from animals, why there is evil and death in the world, and why we get weekends off from work to sit around watching Japanese movies. Similarly, the Japanese creation story, contained in the Kojiki provides the central ancient explanation as to why Japanese do what Japanese do, etc.
It should be no surprise that contemporary publications of the Kojiki include manga versions aimed at educating and entertaining Japanese youth (and cartoon-loving gaijin). The following are scans of a manga version I picked up in Ikebukuro.