Since rings go back to something like 300 BC, their relationship to Christianity is tenuous at best.
The idea of engagement gifts in general goes back so far in history, in so many ways, that it is really hard to say where it started. This may just represent the fact that people like to get gifts, and have liked this for a long time.
Heck, look at the other side, the dowry. That is a tradition that has just about died out, but it still represents a large gift in relationship to a marriage. And since it is referenced in ancient Babylonian texts, I think it has nothing to do with religion, and everything to do with the fact that people like to surround special events with gifts.
Same reasoning seems to go with the bridal shower, wedding gifts, so on and so forth.
Now for something more specific to the Japanese.
In modern Japanese popular culture, IE: Japanese TV shows, the giving of a ring is very common. The start of this trend in ring giving is not new. Even shows that are ten years old have it.
Whether this is life reflecting art, or the reverse, I can not say. But it seems to be the gift of choice that a Japanese female wants when moving the relationship to that point.
So I suggest you break down, buy the ring, and not worry about any preconceived religious connotations that are probably inaccurate.
My Japanese friend doesn't wear her ring but her husband does.
Do what you feel is right without being hung up with any religious thoughts. At worse she can say no. I'd worry less about her and more about her family. Even if she says yes, you still have to win them over.
KikoSoujirou wrote:or you could meet her parents and have a serious conversation with them and ask them for their permission to marry their daughter. but that's a bit more complex.....
I actually did both: proposed to girlfriend in private (in English) the American way, then I asked her parents for permission a while later. Very nerve-wracking and my Japanese was worse then than now, but I managed to pull it off. Big thing is to be honest, humble and just ask "Can we marry?" in Japanese. Really do it the Japanese way and be sincere. It'll work.
When my girlfriend came to visit me in September, I took her to Niagara Falls and asked some random lady to take a couple of pictures of us in front of the Falls. Just before the second picture, I dropped to one knee with the ring and proposed in both Japanese and English as everyone around us freaked out. She freaked out too, of course. Getting married in two months.
I'm proposing to my girlfriend at a high end restaurant tonight. She knows it is coming. But I'm still a bit nervous, because I know all the other patrons will bear witness to this. Not a bad thing I know, but attention in public is not my strong suit. I think I may ask if she will also make me miso soup for the rest of my life, since I like it a lot, and I find the statement very funny. So I will practice right now "Oreno misoshiru wo tsukuttekurenai".
Till death till us part (or at least till the world runs out of miso soup).