Here are a few resources I have read to learn about personal finance:
Bogleheads a wiki about the investment philosophies of John Bogle who made the Vanguard group. They have funds you could purchase and then just forget about with cheap fees, however they aren’t available in Japan. MMM (and I) among many others advise using Index Funds, and Vanguard is the most efficient way to do so. Warren Buffet even said that were he to die, he would recommend Index Funds to his wife.
Rich Dad Poor Dad talks about how to become rich more than anything else but I feel the principles are quite good.
The Four Hour Workweek by Tim Ferriss, and his podcast with over 300 long-form podcasts of which I have listened to the majority. He interviews top performers around the world and tries to find the commonalities between them in his podcast, but the book is more about creating a business/ source of income so that you can live however you like.
How to Own the World is for the UK. It talks about things in Rich Dad Poor Dad but in a bit more detail and for a UK market. I found it useful because it explained things like bonds that I had no idea about.
A Random Walk Down Wall Street teaches about the logic behind the investment strategies to beat the majority of financial planners in the market (by buying the market through Index Funds). It is very technical, but very logical.
Also, Japan has its own RetireJapan blog too, by Ben Shearon who lives in Sendai, although I have never met him. He basically reiterates what others have to say, but also has useful links for retirement tools in Japan.