Short answer
Shinto's oldest books do not claim to be a word from God (﷾). They are court records. The Kojiki's Preface says the Heavenly Sovereign (the emperor) ordered the old chronicles and family records corrected. It says they "deviate from exact truth, and are mostly amplified by empty falsehoods". The Nihon Shoki gives one account of the sun-kami's birth in its main text and sets others beside it, without ruling them out. Those compilers were honest about what they had: a record of what people said. A record of what people remembered, with no messenger who says he speaks for God (﷾), cannot tell us what the Creator wants. Islam answers with a Book that names its speaker, the Lord of the Worlds, and invites everyone to test that claim (2:23). The full explanation sets out each step.
Full explanation
How the Kojiki says it was made
The Kojiki, the "Record of Ancient Matters", is one of the two oldest books of Japan's ancient past. Its Preface was written by the court official Futo no Yasumaro. It says the Heavenly Sovereign commanded that the chronicles of the emperors and the old words held by the families be examined. He had heard that they deviate from exact truth. This is his judgement of those other records, not of the Kojiki. He wanted the falsehoods erased and the truth determined. Later an Empress commanded Yasumaro to select and record the old words. He presented the book in the fifth year of Wa-dō (712) and calls his work obedience to the Decree. Chamberlain's 1882 English renders kami, the sacred beings of Shinto, as "Deity". Shinto scholars explain that kami are not "gods" in the Western sense, so this page keeps Chamberlain's word only inside his quotations.
“I hear that the chronicles of the emperors and likewise the original words in the possession of the various families deviate from exact truth, and are mostly amplified by empty falsehoods.”
“So now I desire to have the chronicles of the emperors selected and recorded, and the old words examined and ascertained, falsehoods being erased and the truth determined”
“regretting the errors in the old words, and wishing to correct the misstatements in the former chronicles, She, on the eighteenth day of the ninth moon of the fourth year of Wa-dō, commanded me Yasumaro”
“Reverently presented by the Court Noble Futo no Yasumaro, an Officer of the Upper Division of the First Class of the Fifth Rank and of the Fifth Order of Merit, on the 28th day of the first moon of the fifth year of Wa-dō.”
“In reverent obedience to the contents of the Decree, I have made a careful choice.”
A Kokugakuin University paper on how kami is understood. It notes that kami is usually translated "god", but that it is often claimed that the Japanese word and the English word are quite different concepts, and it contrasts the monotheism of the Jewish and Christian tradition with the polytheistic ideas of Shinto.
A Kokugakuin University paper on the kami concept. It calls "God" an inapt translation of kami, and says the kami idea does not point to a principle or being apart from creation but to a quality of being that takes part in the unity of existence. It quotes Ueda Kenji that both the Nihon Shoki and the Kojiki speak of a preexisting substance from which the kami came to be. It reports Ueda Kenji's view that the earliest Japanese myths lack any creator deity.
Where the Kojiki says its knowledge came from
The Preface names the sources of what the book knows. Knowledge of the beginning, it says, comes by relying on the original teaching and by trusting the former sages. A retainer, Hiyeda no Are, was commanded to learn by heart the genealogies of the emperors and the words of former ages. The court then examined and corrected the old words. These are sources carried by memory and judged by the court. The Preface does not say who gave the original teaching. It does not present the book as a message handed down to a man from above.
“So in the dimness of the great commencement, we, by relying on the original teaching, learn the time of the conception of the earth and of the birth of islands; in the remoteness of the original beginning, we, by trusting the former sages, perceive the era of the genesis of Deities and of the establishment of men.”
“Forthwith Are was commanded to learn by heart the genealogies of the emperors, and likewise the words of former ages.”
“So now I desire to have the chronicles of the emperors selected and recorded, and the old words examined and ascertained, falsehoods being erased and the truth determined”
The Nihon Shoki sets the accounts side by side
The Nihon Shoki, in Aston's English the "Nihongi" or Chronicles of Japan, is the other great early history. Its first two books, the Age of the Gods, often stop to give another version. A paragraph that begins "In one writing it is said" introduces a different account. In Books 1 and 2 of the site's file, 56 paragraphs begin that way. Take the birth of the sun-kami, whom Aston calls the Sun-Goddess and Chamberlain calls the Heaven-Shining-Great-August-Deity. She is Amaterasu. Paragraph 52 says that the pair Izanagi and Izanami together produced her. Paragraph 64, one of the "In one writing" accounts, says she came from a white-copper mirror in Izanagi's left hand. Paragraph 81 says a Deity was produced by his washing his left eye. That is also the Kojiki's account. The compilers give one account in the main text and set the others beside it, without ruling them out.
“They then together produced the Sun-Goddess, who was called Oho-hiru-me no muchi.”
“In one writing it is said:—"Izanagi no Mikoto said: 'I wish to procreate the precious child who is to rule the world.' He therefore took in his left hand a white-copper mirror, upon which a Deity was produced from it called Oho-hiru-me no Mikoto.”
“Thereafter, a Deity was produced by his washing his left eye, which was called Ama-terasu-no-oho-Kami.”
“The name of the Deity that was born as he thereupon washed his left august eye was the Heaven-Shining-Great-August-Deity.”
Two plain questions to ask of any book
Ask two things of any book that claims to come from the Creator. Does it say who is speaking? Does it invite anyone to check the claim? These are the questions the Qur'an answers about itself, and Islam holds that it passes them. The Kojiki answers the first question in its own Preface. The speakers are a court official, a sovereign's command, the old words and the former sages. It makes no claim to be the Creator's word, so it sets no test for such a claim. That is not a fault in the book. It is what the Kojiki says it is, a record. But a record of what people said needs a messenger from the Creator behind it. Without one, it cannot tell us what the Maker of heaven and earth wants of us.
“I hear that the chronicles of the emperors and likewise the original words in the possession of the various families deviate from exact truth, and are mostly amplified by empty falsehoods.”
“In reverent obedience to the contents of the Decree, I have made a careful choice.”
“So in the dimness of the great commencement, we, by relying on the original teaching, learn the time of the conception of the earth and of the birth of islands; in the remoteness of the original beginning, we, by trusting the former sages, perceive the era of the genesis of Deities and of the establishment of men.”
“And if ye are in doubt as to what We have revealed from time to time to Our servant, then produce a Sura like thereunto; and call your witnesses or helpers (If there are any) besides Allah, if your (doubts) are true.”
“It is not the word of a poet: little it is ye believe! Nor is it the word of a soothsayer: little admonition it is ye receive. (This is) a Message sent down from the Lord of the Worlds.”
What the Qur'an says about itself
The Qur'an names its speaker. It says it is not the word of a poet or a soothsayer, but a Message sent down from the Lord of the Worlds. In the verse that sets its challenge, God (﷾) speaks of what He has revealed to His servant. It tells anyone in doubt to produce a Sura like it. Elsewhere it says that had it been from other than Allah (﷾), people would have found much discrepancy in it. Both are open to any reader. The pages on the Qur'an's challenge, on contradictions and on how to test a scripture give the evidence that Islam says it stands.
“It is not the word of a poet: little it is ye believe! Nor is it the word of a soothsayer: little admonition it is ye receive. (This is) a Message sent down from the Lord of the Worlds.”
“And if ye are in doubt as to what We have revealed from time to time to Our servant, then produce a Sura like thereunto; and call your witnesses or helpers (If there are any) besides Allah, if your (doubts) are true.”
“Do they not consider the Qur'an (with care)? Had it been from other Than Allah, they would surely have found therein Much discrepancy.”
“Say: "If the whole of mankind and Jinns were to gather together to produce the like of this Qur'an, they could not produce the like thereof, even if they backed up each other with help and support.”
What a record cannot answer
A court record can tell what people said about the beginning. With no messenger from the Creator behind it, it cannot tell what He wants of us, or what comes after death. The Qur'an asks who made them (52:35-36), and says man is not left without purpose (75:36). If He wants anything of us, He must have told us, and the telling must be something we can check. Islam does not say any people was left alone. The Qur'an says every people had a warner (35:24; 16:36). It names none for Japan, and the Kojiki does not claim to record one. What Islam asks is that the word God sent to all mankind be tested and read.
“Were they created of nothing, or were they themselves the creators? Or did they create the heavens and the earth? Nay, they have no firm belief.”
“Does man think that he will be left uncontrolled, (without purpose)?”
“Verily We have sent thee in truth, as a bearer of glad tidings, and as a warner: and there never was a people, without a warner having lived among them (in the past).”
“For We assuredly sent amongst every People a messenger, (with the Command), "Serve Allah, and eschew Evil": of the People were some whom Allah guided, and some on whom error became inevitably (established). So travel through the earth, and see what was the end of those who denied (the Truth).”
Where thanks goes, and an invitation
Many people in Japan say itadakimasu before a meal, a small custom of thanks. Islam says who the thanks finally belongs to: the One who gave us hearing, sight and understanding, that we may give thanks (16:78). Islam is a whole way of life (deen), and it begins with that thanks and with knowing how He asked to be thanked. So Islam asks the reader to do for the Qur'an what it asks of anyone. Read it in a translation you trust, and ask whether it is from the Lord of the Worlds. Try its challenge, and look for the discrepancy it says you will not find. If it is God's (﷾) word, then following the last Prophet (ﷺ) who brought it is the way He asks us to live.
“It is He Who brought you forth from the wombs of your mothers when ye knew nothing; and He gave you hearing and sight and intelligence and affections: that ye may give thanks (to Allah).”
“And if ye are in doubt as to what We have revealed from time to time to Our servant, then produce a Sura like thereunto; and call your witnesses or helpers (If there are any) besides Allah, if your (doubts) are true.”
“Do they not consider the Qur'an (with care)? Had it been from other Than Allah, they would surely have found therein Much discrepancy.”
Point by point
Kojiki, Preface, paragraph 4 — the Heavenly Sovereign's command
“I hear that the chronicles of the emperors and likewise the original words in the possession of the various families deviate from exact truth, and are mostly amplified by empty falsehoods.”
Cited for
You quote "empty falsehoods" to say the Kojiki calls itself false.
The response
No. The Preface says this of the older chronicles and family records the court set out to correct, not of the Kojiki. This page quotes it only to show how the book was made.
Where it lands — The words are the Heavenly Sovereign's judgement on earlier records. They show a court correcting records, which is what the Preface says the Kojiki is.
Qur'an 75:16-19 — Surat al-Qiyama (The Resurrection), verses 16-19
“Move not thy tongue concerning the (Qur'an) to make haste therewith. It is for Us to collect it and to promulgate it: But when We have promulgated it, follow thou its recital (as promulgated): Nay more, it is for Us to explain it (and make it clear):”
Cited for
The Kojiki was edited at an emperor's order, and other books have had editors too, so this cannot count against it.
The response
This page does not count it against the Kojiki. The Preface presents the book as an editor's work, and that is honest. The Qur'an claims something different for itself: a Message sent down from the Lord of the Worlds (69:43). Its gathering and explaining are God's (﷾) work (75:16-19). The Qur'an was memorised and written down in the Prophet's (ﷺ) lifetime. Abu Hurayra reported that the angel Gabriel went over the Qur'an with the Prophet (ﷺ) once every year. In the year he died, Gabriel did so twice (Bukhari 4998). The page "How was the Qur'an preserved?" gives the evidence.
Where it lands — The two books describe their own origin differently. The Kojiki says it is a court's record. The Qur'an says it is a Message from the Lord of the Worlds, and invites the test.
Kojiki, Preface, paragraph 4 — Hiyeda no Are
“Forthwith Are was commanded to learn by heart the genealogies of the emperors, and likewise the words of former ages.”
Cited for
The Kojiki came from the memory of Hiyeda no Are, and the Qur'an was memorised too. So your test cannot tell them apart.
The response
Memory carries words. It does not say who spoke them. The Preface says Are learned the genealogies of the emperors and the words of former ages. The Qur'an says its words are a Message from the Lord of the Worlds (69:43), and invites the test (2:23; 4:82). The test asks what a book claims and whether the claim stands up, not how the book was carried.
Where it lands — Both were remembered, but only the Qur'an claims a divine speaker and offers a test of the claim.
Encyclopedia of Shinto: Kamigakari, takusen
Explains kamigakari, the possession of a person by a kami, which is often followed by takusen, an oracle in which the possessed person serves as a medium to pass on the kami's will. A kami may also make its will known in a dream. It notes that the Kojiki and the Nihon Shoki record an example, and that such oracles were later seen as a way of learning the divine will.
Cited for
The old books record kami making their will known through oracles. Motoori Norinaga read the Kojiki's accounts as things that really happened.
The response
Granted that the books report kami speaking, through a person or in a story. They report it as told by others, and sometimes set versions side by side. Motoori trusted the Kojiki as a record, and its Preface names its sources: the old words and the former sages. Neither book says it comes from the Maker of heaven and earth, or invites a test of that claim. By the books' own account the kami came into being within the world. The Qur'an names its speaker as the Lord of the Worlds and sets the test (69:43; 2:23).
Where it lands — Reported words of kami are not a Book from the Creator that names Him and invites the test.
Qur'an 69:41-43 — Surat al-Haqqa (The Reality), verses 41-43
“It is not the word of a poet: little it is ye believe! Nor is it the word of a soothsayer: little admonition it is ye receive. (This is) a Message sent down from the Lord of the Worlds.”
Cited for
Hadith collections give different versions of events too, so variants are normal in a faithful record.
The response
They are. Hadith are reports of what the Prophet (ﷺ) said and did, each with a named chain of narrators that scholars grade. Behind them stands a messenger who said he spoke from God (﷾). The Qur'an says he did not speak from his own desire (53:3-4). The Qur'an itself is one Book, which names its speaker and is open to testing (69:43; 4:82).
Where it lands — Reports about the Prophet (ﷺ) are weighed by their chains, and a messenger stands behind them. The Qur'an is the Message itself, and it is one Book.
Qur'an 23:12-14 — Surat al-Mu'minun (The Believers), verses 12-14
“Man We did create from a quintessence (of clay); Then We placed him as (a drop of) sperm in a place of rest, firmly fixed; Then We made the sperm into a clot of congealed blood; then of that clot We made a (foetus) lump; then we made out of that lump bones and clothed the bones with flesh; then we developed out of it another creature. So blessed be Allah, the best to create!”
Cited for
The Qur'an tells man's creation in different ways (clay, dust, a drop), just as the Nihon Shoki tells the sun-kami's birth in different ways.
The response
The Qur'an names the materials and stages of one account. The first man was made of dust (3:59), and the Qur'an describes man's making from clay through stages that begin with a drop (23:12-14). It does not set rival accounts side by side and leave the reader to choose. The page on contradictions answers this in detail.
Where it lands — One Book names the stages of one creation. A compiler who lists rival versions he could not choose between is doing something else.
Perspectives
Shinto: lived practice, with old records of the kami
Shinto does not teach that the Kojiki or the Nihon Shoki is a revelation. It honours them as the oldest records of the age of the kami. It keeps its customs alive in festival, prayer and purification more than in reading.
The Kojiki and the Nihon Shoki are records of the age of the kami, not scripture. Shinto is lived, so it has no need of a revealed book.
Rebuttal
Grant it: the books say they are records. Then practice alone cannot say what the Creator wants or what comes after death. Islam offers a Book that names its speaker and invites testing (2:23; 69:43).
The Kojiki was written to erase falsehood and fix the truth. So, they say, it is a careful record of what the ancients knew.
Rebuttal
Grant that it was made with care. The Preface describes the method as examining old words and erasing falsehoods. That is how a record is made, not how a message arrives.
The Nihon Shoki sets different versions side by side. This shows honest scholarship, since it keeps every tradition it received.
Rebuttal
Grant it, and honour it. Honest compilers gave one account in the main text and set the others beside it, without ruling them out. That shows a faithful record of what was said, not a message from the Creator.
The old stories, such as the accounts of the sun-kami's birth, are symbolic. They teach lessons about nature and community, and need not be read as a word from God.
Rebuttal
Symbols need a key. A record that does not say who speaks cannot say what its symbols mean, so each reader supplies a key. Without a word from God (﷾), no one can say whose key is right. The Qur'an was explained by the one who brought it (16:44).
Kami are not "gods" in the Western sense, so the question of a word from God does not arise.
Rebuttal
Grant it. Then ask the question without the word "god". Someone made heaven and earth (52:35-36), and man is not left without purpose (75:36). Has He told us what He wants?
What the two books say about themselves
The Kojiki's Preface presents the book as a court record, made by command and chosen with care. The Nihon Shoki gives several accounts of the same events.
The Kojiki's Preface says the Heavenly Sovereign gave a command. The chronicles of the emperors and the old words of the families were to be examined and corrected.
An Empress commanded Yasumaro to select and record the old words. He presented the book in the fifth year of Wa-dō (712) and calls his work obedience to the Decree.
The Preface names the original teaching, the old words and the former sages as its sources. It does not present the book as a message handed down to a man from above.
The Nihon Shoki gives three accounts of the sun-kami's birth: one in its main text and two set beside it, none ruled out. One is the Kojiki's account.
The Islamic perspective
Islam says the Creator has spoken, in a Book that names its speaker and invites testing. Shinto's records are honest records, and do not claim to be that.
The Qur'an names its speaker. It calls itself a Message sent down from the Lord of the Worlds.
The Qur'an invites the test. It tells anyone in doubt to produce a Sura like it. It says that had it come from other than Allah (﷾) it would hold much discrepancy.
Muslims hold that the Qur'an passes the tests it sets for itself. The pages on the Qur'an's challenge and on contradictions give the evidence.
Someone made heaven and earth, and man is not left without purpose. So a record of what people said, with no messenger from Him, cannot be all that the Creator gave us.
Islam does not say any people was left alone. Every people had a warner, though the Qur'an names none for Japan.
Thanks belongs to the One who gave us hearing, sight and understanding. Islam is the whole way of life (deen) that answers Him.