I've been studying up on Japanese WWII firearms recently, and when it comes to rifles my go-to resource is Fred Honeycutt's book Military Rifles of Japan 1897-1945. It isn't the newest book on the subject, nor does it have as much information on specific types as the more focused volumes that have come out since, but it is an excellent compromise between cost and comprehensiveness. Honeycutt covers all the major Japanese rifles from the Type 30 to the Type 99, plus the last-ditch substitute rifles, experimental semiauto designs, sniper rifles, and more. He covers the different nomenclature used to identify Japanese arms, the arsenals that produced them, and the elements like series kanji that are unique to Japanese weaponry. His photos, although in black and white, are clear and effective. More than any other nation, Japan's rifle production during WWII exhibits a traceable gradual decline as the war progressed, which I find fascinating to follow - and Honeycutt's book is the best single resource to guide you along the way.