You are wrong here. You will indeed never be Japanese if you haven't both 2 ethnic Japanese parents and raised in Japanese (second-generation raised abroad, for instance in South American are out). You can't rewrite all your DNA and go back in time to have a Japanese education in Japan.

The real issue is why caring so much about "becoming" Japanese? You can integrate in Japanese society as a foreigner, and being treated as an outsider also has its perks. Typically you are not expected to follow some of the rules, and thus has less bullshit to deal with. Just be careful of not becoming too good in Japanese (or at least pretend not to be), so you can maximize the benefits of speaking Japanese while minimizing the expectations.