What is the general and golden rule to applying Japanese citizenship?

I have never hear of a foreigner getting it
If a person lives here for 5-10 years and contributes to the society and shows that they are settling here permanently, they can apply for "permanent resident" status...

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Not necessarily, samurai8...
Yes, only a few people have told me that it is difficult to apply for Japanese Citizenship but I think the best of all, as long as you contribute to their society and just at least stay there for 5-10 years approx. then you'll be able to obtain one. I think us foreigners hardly can get into it, because even if we live there long enough to experience Japan, probably most of the time, foreigners still seem to not get the what they expect of us...

But hopefully, since I'm still a teenage, willing to live there in future, I just hope that it'll somewhat change in the future!

But I have heard that there is a proposal to change some of the regulations in Japan of migration, as being proposed by the Liberal Party of the Japanese government.

You are talking about a "resident visa"..
it is not citizenship.

I'm a permanent resident and I don't think I'll bother with becoming a Japanese citizen as I don't want to give up my own nationality and passport. Japan doesn't allow dual citizenship (last time i checked) and I don't see any extra benefit to myself or Japan by jumping though the hoops of becoming a citizen. It may be something that others want but not me. It is possible and one does not have to be famous or a sports star. David Aldwinkle has a lot of advice on this but I think it best not to post too much. Perhaps people can Google if interested.
PS: If a persons request for citizenship is declined there is no ownus on the Japanese government to explain why it was declined.