It is fair to say that celebrating Christmas is an established part of Japanese culture.
On the other hand, there are few Christians in Japan who have gone through "rites of passage" such as baptism, and the majority of Christians are foreign nationals, who are estimated to be about 2% of the population.

Logically, "Christmas in Japan is 'heresy,'" and there must be a certain number of people who think so. I was told at the age of 3 that "savior was born," and without much question, I found myself already an elderly person.

First of all, if I had to describe Christmas in Japan in one word, it would be "cheerful, colorful, charming and cute.
I feel that this goes along with what I consider "orthodox theology," that is, "the Savior who once gave himself to free us from sin has come to this world, and we commemorate him and look forward to his second coming. Of course, there are many cultures in the modern world that hold simple and quiet worship services, but there are also many Christian churches that are "cheerful, colorful, and charming," which I observe as the majority (not that that makes them great at all).

Although I have not researched it properly, apart from the "Dai Nihon Shi" (History of Japan), which draws on the "authentic history" compiled very recently, my impression from buried historical documents, art works, and contemporary literature, mainly diaries, is that from the so-called Warring States Period to the Jomon Period before that, Honcho culture was "bright, gorgeous, charming, and cute". cheerful, colorful, charming, and cute.

It is a matter of course that the Honcho culture of "cheerful, colorful, and charming" has existed as a tradition since the Jomon period, and there is no room for any kind of "law of cause and effect" to be added to it. This is just my own opinion.