So whilst reading through the thread, I do think the idea is ASB, but as others have pointed out there might be some more parallels that could be made with the UK.
I've talked before about the potential for greater syncretism in early Christianity. Perhaps with a less united church (or a church that gains more unity later), Celtic Christianity could become very divergent.
Although not treated as such OTL because of the strong Catholic identity of OTL Ireland, the Book of Invasions has all the material you would need for a pagan-syncretic Christianity as (if taken as Gospel), it technically portrays a goddess (Danu) as well as a god, allowing for an almost Wiccan Christianity with a charismatic enough preacher that chooses to take it as gospel (which itself wouldn't be too strange either as the text already integrates Abrahamic Mythology).
What this means is that whilst directly Japanese culture is impossible, Britain seeing itself as a literally holy island, with a culture quite "weird" compared to a mainland which (in a TL of a less united church might be more "secular" like China) is somehow more united.
Might be ASB, (for lack of a better term as my term "Shit Throwing Napoleon" hasn't caught on) but its the closest I could come up with.
[For anyone wondering about the whole "weird" thing, Japanese versions of the mainland religions were often considered strange or sometimes even offensive by their continental counterparts, such as Japanese Buddhism's embracing of the term "death" to describe being in a state of Satori, or its adoption of Confucian culture to advocate a more effeminate man in the Heian period].