All right, time to set the record straight here.
Almost twenty years ago I intensively studied Japanese language and culture planning to spend the rest of my life there. It didn't exactly play out like that, but it was an interesting experience.
The vast majority of Japanese people are very friendly to white people and will be nice to you. You're unlikely to experience anything more than the most minor "microaggressions" from anybody under the age of 50. So you don't have to worry there. The language is not really that hard, there are few sounds, it's highly cohesive and internally consistent, and really the only hard part is the large number of Chinese characters you need to pick up to become fluent, although the most commonly used characters don't take that long to learn. Working through college level textbooks you can be close to fluent in a few years, like I did.
However, this is very different from assimilating into Japanese culture. You won't. You'll always stick out. This is almost never because Japanese people are trying to exclude you, but the way Japanese think is very distinct, very eastern, and it's not something you get from book learning. This causes invisible barriers making it hard to form deep friendships and relationships in general, especially with normal Japanese people who aren't all starry-eyed about the West. It's this latter category that will likely make up most of your Japanese friends - and potential love interests - thus giving you a skewed perspective from people not really representative of the norm. The western fanboy/girl also tends to get pretty annoying after a while. Not coincidentally, lots of white guy-Japanese woman marriages don't go so well.
Many things said about Japan are true - high social trust, low crime, low degeneracy/conservative culture, and all that. Could be a good place to be when things go south. On the surface, you can live an enjoyable, comfortable life in Japan, but attaining depth and a true sense of belonging there is challenging and usually not possible for most westerners. "Rootedness," as Simone Weil described it, a fundamental but rarely recognized human need, will evade you. This is why most long-term resident Westerners in Japan tend to be miserable, drunk, and/or largely detached from Japanese culture and almost always resort to living in a bubble with other foreigners. This can be a legitimate survival strategy, but bad for prolonged periods. Being rooted as a foreigner in Japan isn't totally impossible, but it's quite unlikely, so don't bank on it.
Japan is also a spiritual vacuum, an incredibly materialistic place where people have been catechized ever since the post-war period out of any contemplation of higher things in favor of riches, stuff, achievement, and the various passions. As a Christian you will often feel alone, even if you attend some church and have Christian friends there. So that's something else to be aware of.
Also, Japanese women are very overrated. You see the prettiest examples in entertainment and media, just like anywhere else, and the average girl, though less fat than her western counterparts, is not as dazzling as you may expect, and have picked up various negative behavioral attributes through osmosis from western entertainment, which Japanese women absolutely love. Beyond all that, you'll run into big issues with non-verbal communication and things like that. I ended up marrying a (white) Brazilian. I suggest you do that instead.
