Short answer
Islam's answer is that worship is not to be shared out. It belongs to the One who made us, so prayers, offerings and bows of worship go to Him alone. Many families in Japan take part in both traditions. A baby is taken to a shrine, New Year brings a visit to a shrine or temple, and most funerals use Buddhist rites. Shinto honours kami, sacred powers that scholars of Shinto say are not "gods" in the Western sense. Kami and Buddhas were combined in Japan's shrines and temples from the eighth century until 1868. Islam asks a question beneath both: who made heaven and earth, and who hears every prayer? Its answer is Allah (﷾) alone. The Qur'an's words "To you be your Way, and to me mine" (109:6) are about not mixing worship. Islam offers one Lord over birth, life and death, and a complete way of life.
Full explanation
Worship belongs to One
Islam begins with one principle. Worship belongs to the One who made us, and to no one beside Him. A Muslim says in every prayer: Thee do we worship, and Thine aid we seek. The Qur'an says the places of worship are for Allah (﷾), so invoke no one along with Him. It tells the Prophet (ﷺ) to say that his prayer, his sacrifice, his life and his death are for Allah (﷾), who has no partner. It asks: is it not to Allah (﷾) that sincere devotion is due? So the question is not how many places a person visits. It is to whom the prayers, offerings and bows of worship are given.
“Thee do we worship, and Thine aid we seek.”
“"And the places of worship are for Allah (alone): So invoke not any one along with Allah;”
“Say: "Truly, my prayer and my service of sacrifice, my life and my death, are (all) for Allah, the Cherisher of the Worlds: No partner hath He: this am I commanded, and I am the first of those who bow to His will.”
“Is it not to Allah that sincere devotion is due? But those who take for protectors other than Allah (say): "We only serve them in order that they may bring us nearer to Allah." Truly Allah will judge between them in that wherein they differ. But Allah guides not such as are false and ungrateful.”
A shrine and a temple in one life
Many Japanese families meet both in the course of a life. Kami are the sacred powers Shinto honours, and scholars of Shinto say they are not "gods" in the Western sense. About a month after a birth, many take the baby to the shrine of the local kami, to pray for the child's happy growth. At New Year many visit a shrine or a temple, often at midnight to hear the temple bells. When someone dies, the great majority of funerals in Japan use Buddhist rites. Buddhist funerals became the rule in the Edo period (1603-1868), when everyone had to register with a Buddhist temple.
The Encyclopedia of Shinto describes hatsumiyamode, or miyamairi, as a baby's first visit to the shrine of the local tutelary kami. It usually falls about a month after birth. The family prays for the child's happy growth, and the visit once marked the child's welcome as a new parishioner.
The Encyclopedia of Shinto defines hatsumode as a visit to a shrine or a temple at the beginning of the new year. Many people go from midnight on New Year's Eve, to hear the temple bells ring in the year and make their visit there.
The Encyclopedia of Shinto explains that Buddhist clergy took part in Japanese funerals from the end of the seventh century. Their part peaked in the Edo period, when everyone had to register with a Buddhist temple and funerals were held in the Buddhist style. Shinto funerals became one of the options in the modern period. It says Buddhist rites still account for the great majority of Japanese funerals.
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.
How kami and Buddhas were combined, and then separated
Buddhism reached Japan in the sixth century. From the eighth century, kami and Buddhas were combined in shrines and temples, and this lasted until 1868. It grew over centuries through the teaching of Buddhist monks and the practice of shrines. Temples rose within shrine grounds, and sutras (Buddhist scriptures) were read before the kami. Monks taught honji suijaku: the kami are "traces" of Buddhas and bodhisattvas, who are their true form. (A bodhisattva is a being on the way to becoming a Buddha, who works to save others.) By the end of the Heian period in 1185, each shrine's kami had been assigned a Buddhist original. The separation was different. In the spring of 1868 the new government issued the separation edicts (shinbutsu hanzenrei). Its Bureau of Divinities (Jingi Jimukyoku) worked to carry them out.
The Encyclopedia of Shinto describes shinbutsu shugo, the combination of kami and buddhas, shrines and temples, and their priests, as having its roots in the Nara Period (710-94). Buddhism, which reached Japan in the sixth century, combined steadily with Shinto until the honji suijaku theory of the medieval period. Temples rose within shrine grounds, sutras were read at shrines, kami were called bodhisattvas, and priests in Buddhist dress led shrine rites. In the early modern period Kokugaku thinkers and shrine priests called for shrines to return to their original form. The Restoration government of 1868 issued the separation edicts on the seventeenth day of the third month, with further orders later that month and in the months that followed.
The Encyclopedia of Shinto defines honji suijaku as the idea that Buddhist deities appear for a time as Shinto kami, to save living beings in Japan. The kami are their manifestations (suijaku, "traces"), and the Buddhist deities are the kami's original ground (honji), their true form. The terms come from Tendai Buddhism. It used them, in the Life Span of the Tathagata chapter of the Lotus Sutra, to tell apart the eternal Shakyamuni (kuonjitsujo, 'truly attained in the distant past') and the historical Shakyamuni. The first Japanese reference is in a work thought to date from about 825. The Enryaku-ji monk Eryo was the first to use suijaku of the kami. By the end of the Heian period, the kami of each shrine had been assigned a buddha or bodhisattva as its honji.
A study of the separation at one shrine. It names the government decree of 1868 the shinbutsu bunri rei or shinbutsu hanzen rei, which ordered the separation of the gods and Buddhas at all Shinto shrines. It says this ended a tradition of about a thousand years in which Buddhism and Shinto were combined.
The Encyclopedia of Shinto says the new government set up a Shinto Section (Jingi Jimuka) in the first month of 1868. The next month it was expanded into the Bureau of Divinities (Jingi Jimukyoku). The bureau worked to carry out the separation of Buddhism from Shinto. Under the separation order, Buddhist elements were to be removed from shrines, and Buddhist priests were removed from the leadership of shrines.
Not which of the two, but to whom
Islam does not ask which of the two to choose. It asks a question beneath both: who made heaven and earth? The Kojiki, in Chamberlain's English, calls the kami "Deities". It says its first kami came into being when heaven and earth began. The Buddhas named as the kami's originals differ from shrine to shrine, and Buddhist teachers do not call them the Creator. The words honji and suijaku come from the Tendai school's teaching on the Lotus Sutra. In its chapter on the Buddha's lifespan, the Buddha says his life is endless, and that he acquired it "after previously following a due course". What comes into being, or acquires its life, is not the Maker of heaven and earth. The Qur'an asks whether people were created of nothing, or were themselves the creators. Its answer is that Allah (﷾) is the Creator of all things, and worship belongs to Him alone.
“The names of the Deities that were born in the Plain of High Heaven when the Heaven and Earth began were the Deity Master-of-the-August-Centre-of-Heaven, next the High-August-Producing-Wondrous Deity, next the Divine-Producing-Wondrous-Deity. These three Deities were all Deities born alone, and hid their persons.”
The Encyclopedia of Shinto defines honji suijaku as the idea that Buddhist deities appear for a time as Shinto kami, to save living beings in Japan. The kami are their manifestations (suijaku, "traces"), and the Buddhist deities are the kami's original ground (honji), their true form. The terms come from Tendai Buddhism. It used them, in the Life Span of the Tathagata chapter of the Lotus Sutra, to tell apart the eternal Shakyamuni (kuonjitsujo, 'truly attained in the distant past') and the historical Shakyamuni. The first Japanese reference is in a work thought to date from about 825. The Enryaku-ji monk Eryo was the first to use suijaku of the kami. By the end of the Heian period, the kami of each shrine had been assigned a buddha or bodhisattva as its honji.
“the duration of my life is as long as an endless period; I have acquired it after previously following a due course.”
“I am the Divinity, the Great Divinity, the Vanquisher, the Unvanquished, the Universal Seer, the Wielder of Power, God Almighty, the Maker, the Creator, the First, the Begetter, the Controller, the Father of those who have been born and those yet to be born. These beings were created by me!”
“Everything this individual person experiences—pleasurable, painful, or neutral—is because of God Almighty’s creation.”
“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.”
“Allah is the Creator of all things, and He is the Guardian and Disposer of all affairs.”
“"And the places of worship are for Allah (alone): So invoke not any one along with Allah;”
"To you be your Way, and to me mine"
The Qur'an has a short surah on this very question. It says: I worship not that which ye worship, nor will ye worship that which I worship. It ends: To you be your Way, and to me mine. Ibn Kathir says the surah disowns the worship of the idolaters and commands sincerity in worship. Al-Tabari reports that it answered an offer to take turns: one year for their gods, one year for Allah (﷾). So the verse is about not mixing worship. Islam forces no one to accept it, for the Qur'an also says there is no compulsion in religion.
“Say: O ye that reject Faith! I worship not that which ye worship, Nor will ye worship that which I worship. And I will not worship that which ye have been wont to worship, Nor will ye worship that which I worship. To you be your Way, and to me mine.”
Ibn Kathir says this surah disowns the worship of the idolaters and commands sincerity in worship. He mentions a report, introduced with "it was said", that they invited the Prophet (ﷺ) to worship their idols for a year while they worshipped his Lord for a year. The surah came down, telling him to disown their way entirely. On "To you be your Way, and to me mine", he sets beside it 10:41: "My work to me, and yours to you".
Al-Tabari says the idolaters of the Prophet's (ﷺ) people offered to worship Allah for a year if he would worship their gods for a year, and the surah was God's answer. He gives early reports to this effect. In one, through Ibn Ishaq, leaders of Quraysh say: let us worship what you worship, and you worship what we worship, and we will share the whole matter with you.
“Let there be no compulsion in religion: Truth stands out clear from Error: whoever rejects evil and believes in Allah hath grasped the most trustworthy hand-hold, that never breaks. And Allah heareth and knoweth all things.”
A prayer for a newborn
Families who take a baby to a shrine are praying for the child's happy growth. Muslim parents pray for their children too, to God (﷾) alone. The Qur'an tells of the mother of Mary, who commended her newborn daughter to His protection. It also teaches believers to pray: Our Lord, grant us wives and offspring who will be the comfort of our eyes. The care for the child is the same. The prayer goes straight to the One who gives every child life.
The Encyclopedia of Shinto describes hatsumiyamode, or miyamairi, as a baby's first visit to the shrine of the local tutelary kami. It usually falls about a month after birth. The family prays for the child's happy growth, and the visit once marked the child's welcome as a new parishioner.
“When she was delivered, she said: "O my Lord! Behold! I am delivered of a female child!"- and Allah knew best what she brought forth- "And no wise is the male Like the female. I have named her Mary, and I commend her and her offspring to Thy protection from the Evil One, the Rejected."”
“And those who pray, "Our Lord! Grant unto us wives and offspring who will be the comfort of our eyes, and give us (the grace) to lead the righteous."”
One Lord for birth, life and death
In Islam, the same Lord is there at a birth and at a death. The Qur'an says that Allah (﷾) gives both life and death. Allah (﷾) also says He is close, and listens to the prayer of every caller. Islam is a complete way of life: one Creator, prayer, food, family and character together. It asks you to consider the Qur'an with care and see whether it holds together. It also asks you to consider Muhammad (ﷺ), the last Prophet, who was sent to all people.
“Say: "O men! I am sent unto you all, as the Messenger of Allah, to Whom belongeth the dominion of the heavens and the earth: there is no god but He: it is He That giveth both life and death. So believe in Allah and His Messenger, the Unlettered Prophet, who believeth in Allah and His words: follow him that (so) ye may be guided."”
“When My servants ask thee concerning Me, I am indeed close (to them): I listen to the prayer of every suppliant when he calleth on Me: Let them also, with a will, Listen to My call, and believe in Me: That they may walk in the right way.”
“Do they not consider the Qur'an (with care)? Had it been from other Than Allah, they would surely have found therein Much discrepancy.”
“Muhammad is not the father of any of your men, but (he is) the Messenger of Allah, and the Seal of the Prophets: and Allah has full knowledge of all things.”
Five replies answered
Qur'an 109:1-6 — Surat al-Kafirun (The Disbelievers), verses 1-6
“Say: O ye that reject Faith! I worship not that which ye worship, Nor will ye worship that which I worship. And I will not worship that which ye have been wont to worship, Nor will ye worship that which I worship. To you be your Way, and to me mine.”
Cited for
"To you be your Way, and to me mine" means every way is fine, so I can keep both.
The response
The same surah says: I worship not that which ye worship. Ibn Kathir reads it as disowning the idolaters' worship and a command to sincerity. Al-Tabari reports that it answered an offer to take turns in worship. The verse refuses to mix worship, and elsewhere the Qur'an says there is no compulsion in religion.
Where it lands — The verse is about keeping worship unmixed, and the choice to accept Islam is yours.
Encyclopedia of Shinto: Honjisuijakusetsu
The Encyclopedia of Shinto defines honji suijaku as the idea that Buddhist deities appear for a time as Shinto kami, to save living beings in Japan. The kami are their manifestations (suijaku, "traces"), and the Buddhist deities are the kami's original ground (honji), their true form. The terms come from Tendai Buddhism. It used them, in the Life Span of the Tathagata chapter of the Lotus Sutra, to tell apart the eternal Shakyamuni (kuonjitsujo, 'truly attained in the distant past') and the historical Shakyamuni. The first Japanese reference is in a work thought to date from about 825. The Enryaku-ji monk Eryo was the first to use suijaku of the kami. By the end of the Heian period, the kami of each shrine had been assigned a buddha or bodhisattva as its honji.
Cited for
The kami are traces of the Buddhas, so shrine and temple are one devotion.
The response
That teaching joins the two, but it does not make either the Creator. The Kojiki says its kami came into being. The Lotus Sutra's Buddha says he acquired his endless life. A medieval Shinto text calls Amaterasu, revered as the kami of the sun, a form of the cosmic Buddha Dainichi. Kukai, the founder of Shingon Buddhism, taught that the cosmos is Dainichi's body. The Qur'an teaches that the Creator of the heavens and the earth is not what He made: "there is nothing whatever like unto Him". He is "the First", and "He begetteth not, nor is He begotten".
Where it lands — Joining the kami and the Buddhas names no Creator above the world. The Qur'an names Him.
Encyclopedia of Shinto: Shinbutsu Bunri
The Encyclopedia of Shinto describes shinbutsu shugo, the combination of kami and buddhas, shrines and temples, and their priests, as having its roots in the Nara Period (710-94). Buddhism, which reached Japan in the sixth century, combined steadily with Shinto until the honji suijaku theory of the medieval period. Temples rose within shrine grounds, sutras were read at shrines, kami were called bodhisattvas, and priests in Buddhist dress led shrine rites. In the early modern period Kokugaku thinkers and shrine priests called for shrines to return to their original form. The Restoration government of 1868 issued the separation edicts on the seventeenth day of the third month, with further orders later that month and in the months that followed.
Cited for
The separation of 1868 was forced by the state. The true Japanese way is to combine the two.
The response
The combination in shrines and temples grew for about a thousand years, and the separation was a government order. Islam's case does not rest on either. Combined or separated, the question is the same: to whom is worship given?
Where it lands — The history does not change the question. Worship belongs to the One who made us.
Review of Reader and Tanabe, Practically Religious (1998)
A review of Ian Reader and George J. Tanabe Jr., Practically Religious: Worldly Benefits and the Common Religion of Japan (1998). Kisala notes that surveys in Japan show low religious affiliation alongside high religious participation. Reader and Tanabe argue that praying for this-worldly, practical benefits (genze riyaku) is integral to the faith and practice of Shinto and the established Buddhist sects. In their view, kami and buddhas are joined in people's expectation that both can grant such benefits. They distinguish affective from cognitive belief, to explain why people who doubt that amulets work still buy them at shrines and temples.
Cited for
The kami and Buddhas are helpers. They protect my family and bless the year.
The response
Islam teaches that every good and every harm is in Allah's (﷾) hands: if He designs some benefit for you, no one can keep it back. Intercession is real, but all of it belongs to Him and comes only by His leave. So a Muslim asks God (﷾) Himself for the family's health and safety, for He is close and answers every caller.
Where it lands — Every blessing is God's (﷾) to give, and He can be asked directly.
Encyclopedia of Shinto: Shinsosai (Shinto funeral rites)
The Encyclopedia of Shinto explains that Buddhist clergy took part in Japanese funerals from the end of the seventh century. Their part peaked in the Edo period, when everyone had to register with a Buddhist temple and funerals were held in the Buddhist style. Shinto funerals became one of the options in the modern period. It says Buddhist rites still account for the great majority of Japanese funerals.
Cited for
I only keep these customs for my family. I don't really believe in them.
The response
Islam keeps family ties strong, even with parents who are not Muslim. In these customs, what Islam asks is that worship go to God (﷾) alone. Some cases, like a bow of greeting or a family funeral at a temple, need care. The page on family customs explains more, and a qualified scholar can answer your own case.
Where it lands — Family ties stay and grow. Worship goes to God (﷾) alone.
Perspectives
Shinto and Buddhism side by side
Many people in Japan keep shrine customs and Buddhist rites together, as their families have for generations. They see no clash, because each has its own place in life.
Shrine and temple visits are a matter of custom and practice, not belief, so doing both involves no clash.
Rebuttal
Worship is itself a practice. Islam asks to whom the bows, prayers and offerings are given, and gives them all to God (﷾) alone.
Each has its own work: the kami for birth and festivals, the Buddhas for the dead.
Rebuttal
The Qur'an names one Lord who gives both life and death. Birth and death are in the same hands, so one Lord is enough for both.
Shinto honours many kami, so honouring the Buddhas as well takes nothing away.
Rebuttal
Islam holds that sincere devotion is due to Allah (﷾) alone. Worship shared among many is not given wholly to the One who made them all.
The kami and Buddhas are helpers. They protect the family and grant blessings in this life.
Rebuttal
Every blessing is in Allah's (﷾) hands, and no one can hold back what He gives. Intercession is real, but it belongs to Him alone and comes only by His leave. A Muslim asks God (﷾) Himself, for He is close and answers every caller.
Buddhist: honji suijaku
The medieval honji suijaku teaching held that the kami are traces of Buddhas and bodhisattvas, who appear as kami to save living beings in Japan. On this view, honouring both is one devotion.
The kami are manifestations of Buddhas and bodhisattvas, so honouring both is really one devotion.
Rebuttal
Joining them does not make either the Creator. The Kojiki's kami came into being, and the Lotus Sutra's Buddha acquired his endless life. Worship belongs only to the Creator of all things, and neither is He.
Historians: combination and separation
Kami and Buddhas were combined in Japan's shrines and temples from the eighth century until 1868. The combination grew over centuries among monks and shrines; the separation of 1868 was a government order.
The combination of kami and Buddhas had its roots in the Nara period. It grew into honji suijaku in the medieval period.
In the spring of 1868 the new government issued the separation edicts. Its Bureau of Divinities worked to carry them out.
The Islamic perspective
Worship belongs to the One who made heaven and earth, and it is not shared out. Islam asks not which of two traditions to follow, but to whom worship is given. It invites the reader to one Lord of birth, life and death. It asks the reader to weigh the Qur'an and the last Prophet (ﷺ), and offers a complete way of life.
Prayer, offerings and bows of worship belong to Allah (﷾) alone; sincere devotion is due to Him.
The kami of the Kojiki came into being, and the Lotus Sutra's Buddha acquired his endless life. Neither is the Maker of heaven and earth, to whom alone worship is due.
"To you be your Way, and to me mine" is about not mixing worship. No one is forced to accept Islam.
One Lord gives life and death and hears every caller. The Qur'an invites careful reading, and Muhammad (ﷺ) was sent to all people.