Right now... It's Umeyo Hirano's translation of 日本語 (Nihongo, or "The Japanese Language') by Haruhiko Kindaichi - A thoroughly fascinating read about the history and context of the language - from sentance construction to regional dialects, all the way to status and hierarchal intonation. It's also a little, er... Old, and outdated, in some regards - so I would recommend having a vague understanding of sociopolitical tensions in Japan in the late Meiji period - you have to imagine, this book was penned at a time of unruliness and a lack of faith in the future of the language due to a multitude of consecutive events building an ever-growing worry; 1957 is right on the tail end of Japan's brief occupation by American forces after the end of World War II (And, to add on, Japan's occupation of Korea, in which they had struggled to introduce the language in any meaningful way - this is where you can imagine the "Old-fashioned" ideas which I would like you to understand the wider societal context of, lest it fly over your head - this was, in no uncertain terms, not something which one would like to agree upon as a 'boon')
I would reccomend it to scholars of the Japanese language who have passed their N5, and are on their way to an N4 or perhaps N3 this year; it explains the 'long-form' context as to why sentences are built like this, where dialects and hierarchal vocabulary comes from, so on, so forth... But yes, I would recommend you look into some concepts.
A good beginning start understanding the underlying thoughts and feelings of a nation is perhaps to start on this English Language article about the Bankara anti-fashion movement, about pushing against a growing Western influence with a worrying edge of quite-too-deep-rooted nationalistic tendencies; "
Bankara: Meiji Japan’s Anti-Fashion Movement", a short article published by Noah Oskow on Unseen Japan.
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Also, I am now on Volume 14 of Dark Horse publication of Astro Boy.
