[Japanese grammar books]
A very small book, but contains really good insights into the Japanese language and culture.
Although I have been familiar with Japanese culture for so long, I learned so much from this little volume.
And oh was it fun to read it. I learned many things; from 挨拶 (Aisatsu, greetings) to 悪い言葉 (Warui kotoba, bad words), and 謙遜 (Kenson, modesty) to けんか語 (Kenkago, quarrelsome words). It even has a chapter on 早口言葉 (Hayaguchi kotobatongue-twisters)!
I also learned about Japanese traditional games like Hanafuda, Igo, and Jaankenpon.
Highly recommended for those seeking a peek into the Japanese world.