The Japanese creation myths (Kuniumi) are told in the earliest Japanese Chronicles, the Kojiki and the Nihongi. The Kojiki (written by O no Yasumaro in 711-12) is the oldest of the historical texts. The first English translations of the Nihongi and the Kojiki can be found at the Internet Archive:
Nihongi: Chronicles of Japan from the Earliest Times to A.D. 697. Trans. from the original Chinese and Japanese by W. G. Aston. (Transactions and Proceedings of The Japan Society, London, supplement 1). Vol. 1. London: Printed por Kegan Paul, Trench, Trübner & Co, 1896. Online at Internet Archive: https://archive.org/details/nihongichronicl00astogoog
O no Yasumaro. "Kojiki." Wikipedia: The Free Encyclopedia.*
_____. The Kojiki translated by Basil Hall Chamberlain. 199. Online at Sacred Texts.
The Nihongi (Chronicles of Japan), written in Chinese in 720 A.D. takes us through the early centuries of Japanese history, through a mixture of legend, pseudo-chronicle, and historical record, but it begins at the dawn of time, in myth—with a cosmogonic creation story which explains the origin of the Earth, of the gods, of Japan and of the humans. Here are some fragments coming from the Sacred Texts website.
THE NIHONGI - THE AGE OF THE GODS
Of old, Heaven and Earth were not yet separated, and the In and Yo not yet divided. They formed a chaotic mass like an egg which was of obscurely defined limits and contained germs.
The purer and clearer part was thinly drawn out, and formed Heaven, while the heavier and grosser element settled down and became Earth.
The finer element easily became a united body, but the consolidation of the heavy and gross element was accomplished with difficulty.
Heaven was therefore formed first, and Earth was established subsequently.
Thereafter divine beings were produced between them.
Hence it is said that when the world began to be created, the soil of which lands were composed floated about in a manner which might be compared to the floating of a fish sporting on the surface of the water.
At this time a certain thing was produced between Heaven and Earth. It was in form like a reed-shoot. Now this became transformed into a God, and was called Kuni-toko-tachi no Mikoto.
Next there was Kuni no sa-tsuchi no Mikoto, and next Toyo-kumu-nu no Mikoto, in all three deities
These were pure males spontaneously developed by the operation of the principle of Heaven.
In one writing it is said: '"When Heaven and Earth began, a thing existed in the midst of the Void. Its shape may not be described. Within it a deity was spontaneously produced, whose name was Kuni-toko-tachi no Mikoto, also called Kuni-soko-tachi no Mikoto. Next there was Kuni no sa-tsuchi no Mikoto, also called Kuni no sa-tachi no Mikoto. Next there was Toyo-kuni-nushi no Mikoto, also called Toyo-kumu-nu no Mikoto, Toyo-ka-fushi-no no Mikoto, Uki-fu-no-toyo-kahi no Mikoto, Toyo-kuni-no no Mikoto, Toyo-kuhi-no no Mikoto, Ha-ko-kuni-no no Mikoto, or Mi-no no Mikoto."
In one writing it is said: "Of old, when the land was Young and the earth young, it floated about, as it were floating oil. At this time a thing was produced within the land, in shape like a reed-shoot when it sprouts forth. From this there was a deity developed, whose name was Umashi-ashi-kabi-hiko-ji no Mikoto. Next there was Kuni no toko-tachi no Mikoto, and next Kuni no sa-tsuchi no Mikoto."
In one writing it is said: " When Heaven and Earth were in a state of chaos, there was first of all a deity, whose name was Umashi-ashi-kabi-hiko-ji no Mikoto. Next there was Kuni-soko-tachi no Mikoto."
In one writing it is said: "When Heaven and Earth began, there were deities produced together, whose names were, first, Kuni-no-toko-tachi no Mikoto, and next Kuni no satsuchi no Mikoto." It is further stated: "The names of the gods which were produced in the Plain of High Heaven were Ama no mi-naka-nushi no Mikoto, next Taka-mi-musubi no Mikoto, next Kami-mi-musubi no Mikoto."
In one writing it is said: "Before Heaven and Earth were produced, there was something which might be compared to a cloud floating over the sea. It had no place of attachment for its root. In the midst of this a thing was generated which resembled a reed-shoot when it is first produced in the mud. This became straightway transformed into human shape and was called Kuni no toko-tachi no Mikoto."
A passage from Aston's translation of Book 1. He notes the phallic inspiration of the following creation story:
Izanagi no Mikoto and Izanami no Mikoto stood on the floating bridge of Heaven, and held counsel together, saying:
"Is there not a country beneath?"
Thereupon they thrust down the jewel-spear [penis] of Heaven, and groping about therewith found the ocean. The brine which dripped from the point of the spear coagulated and became an island which received the name of Ono-goro-jima.
Cf. the Kojiki's version of this episode. In the following passage, which immediately follows the previous one, we can see a myth comparable to that of Adam and Eve as regards the supremacy of the male sex—with the female initiative being curtailed and male preeminence and activity being asserted in spite of the woman's original readiness to become an agent. The English text also seems to suggest that it is the man who is moving in the "right" way, clockwise, whereas the woman moves to the right, counterclockwise, although this is admittedly ambiguous:
The two Deities thereupon descended and dwelt in this island. Accordingly they wished to become husband and wife together, and to produce countries.
So they made Ono-goro-jima the pillar of the centre of the land.
Now the male deity turning by the left, and the female deity by the right, they went round the pillar of the land separately. When they met together on one side, the female deity spoke first and said: —"How delightful! I have met with a lovely youth." The male deity was displeased, and said: —"I am a man, and by right should have spoken first. How is it that on the contrary thou, a woman, shoulds have been the first to speak? This was unlucky. Let us go round again." Upon this the two deities went back, and having met anew, this time the male deity spoke first, and said: —"How delightful! I have met a lovey maiden."
Then he inquired of the female deity, saying: —"In thy body is there aught formed?" She answered, and said: —"In my body there is a place which is the source of femineity." The male deity said:—"In my body again there is a place which is the source of masculinity. I wish to unite this source-place of my body to the source-place of thy body." Hereupon the male and female first became united as husband and wife.
Now when the time of birth arrived, first of all the island of Ahaji was reckoned as the placenta, and their minds took no pleasure in it. Therefore it received the name of Ahaji no Shima.
Next there was produced the island of Oho-yamato no Toyo-aki-tsu-shima. [Nippon]
Next they produced the island of Iyo no futa-na [Shikoku], and next the island of Tsukushi [Kiushiu]. Next the islands of Oki and Sado were born as twins. This is the prototype of the twin-births which sometimes take place among mankind.
Nest was born the island of Koshi, then the island of Ohoshima, then the island of Kibi no Ko.
Hence first arose the designation of the Oyo-ya-shima country.
Then the island of Tsushima and Iki, with the small islands in various parts, were produced by the coagulation of the foam of salt-water.
The early generations of deities will be engendered by these gods—although their earliest children, the leech and the island of Aha (Foam), are not considered legitimate or well-formed, and are abandoned by their parents. According to the Kojiki, these defective children resulted from the woman having spoken first.