First of all, I must emphasize that the popularity of 'Christian style' marriage ceremony in Japan is VERY recent phenomena that has got the upper hand at first in the late 1990s, as demonstrated by Ishii's study, based mainly on the two statistics conducted respectively by the different wedding/ bridal service companies plus Ishii's own interviews (Ishii 2005: 30-38).

Ishii, originally a religious scholar, casts doubts on how religious this ceremony can actually be, formulating as the following:

'A cross, a virgin road, a person like a pastor and an atmosphere like a church are what they [the majority of the Japanese] need all. and we indeed have little concrete idea how the Japanese actually understand "such an atmosphere like a church"......Compared with 'Shinto style' marriage ceremony, sometimes associated with the stubborn traditionalism, the Japanese may regard instead 'Christian style' as more suitable for a happy ritual representing the consent between two loving individuals'. (Ishii 2005: 74, 77: my translation).

Even the older, 'more traditional' Shinto style marriage, primarily the contract between the two families is a kind of 'invented tradition' under the Imperial Japanese Constitution after the Meiji Restoration (1868), so in fact neither so traditional nor religious than it sounds at a first glance. The familial structures in modern Japan underwent profound changes several times, at first after the Meiji Restoration and then after WWII, and the marriage ceremony and its affiliated 'religions' are also no exceptions to such a trend.

There are some fore-running phenomena of this popularity of alleged Christian marriage in the 1970s and in the 1980s, though, illustrated by Igarashi and Ishii respectively from a different point of view. While Igarashi is an architectural historian, Ishii is a religious scholar.

• According to Igarashi who identifies the direct precursor of the marriage (only) chapel in Japan with those in Las Vegas in USA (Igarashi 2007: 15f.), the first 'commercial' marriage chapel, attached to a party hall or a hotel, in Japan, dates back to 1975. They tend to be modeled after some Gothic-like cathedrals (but sometimes with mistakes), and almost always with the slopes for picture-taking for the bride, clad with long wedding dress. Even some of them in fact resemble the traditional style church buildings in Europe or in USA than the 'actual' church buildings in Japan.
• Ishii also cites an interesting document in his book, a special license granted in March 01, 1975 by the Vatican to the Catholic churches in Japan that allows non-baptized persons to get married in the church (only) in Japan due to the missionary purpose to more wider possible audiences (Ishii 2005: 52-54.), but I can find an only later supplement (not the special licent itself) in 1992 (only in Japanese) in open access. On the other hand, there had been some discussion concerning how to accept the Christian style marriage between non-Christians also among the protestant pastors in the 1980s (Ishii 2005: 51f.).

References (only in Japanese, sorry):

• Taro IGARASHI. The Birth of 'Marriage Chapels' (the church building specially built for the marriage ceremony, often by the wedding/ bridal service company) (Kekkon Shiki Kyokai no Tanjo) [in modern Japan]. Tokyo: Shunshu Sha, 2007.
• Kenji ISHII. The Marriage Ceremony: that makes them happy (Kekkon Shiki: Shiawase wo Tsukuru Gishiki). Tokyo: NHK Books, 2005.
• Kazuko KOIZUMI (ed.). Marriage in Showa Period (Showa no Kekkon). Tokyo: Kawade Shobo Shinsha, 2014.