What you are asking covers a wide area, but I will try ti point you in the right direction.

For the Japanese, there is an excellent online resource is Combinedfleet , which goes into detail about the Life (and death) of the Imperial Japanese Navy in WW2. There is a even section called " Untold Tales of the Imperial Japanese Navy". The two primary operators of that site go out of their way to use JAPANESE sources for their material... If you like their approach (some don't) they also teamed up and wrote a book SHATTERED SWORD about about the pivotal battle of Midway from the Japanese prospective.

Sabaru Sakai was the highest scoring Japanese flying ace who somehow managed to survive the entire war, when most of his contemporaries wound up on the bottom of the Pacific. Later on he became a pacifist and a vocal advocate for Japan coming clean about her war crimes. There are some interviews out there, a little 'google magic' will guide you.

As for the Germans, there is a mountain of information out there. I'll list a couple of favorites: Uboat.net is exactly what is says on the tin and has been around a long time (in internet years) it is a nuts-and-bolts type site, more into facts and tech than telling stories, but is a good start for you own research.

German Generals Talk was written directly from interviews of High-ranking german Officers right after the war ended. it weaves a narrative about what was going on in the collective mind of German Commanders a critical points in the War.

Four Years, Five Fronts is an autobiography of a German soldier who fought on every major front, and did so from Private to Regimental commander. It tends to drag at parts but it is a great insight on battles form the dirt level, especially in the East (against Russia)

Iron Coffins was written by a (former) U-boat commander about his experiences fighting the war under the Atlantic. He does a great job of getting you "into the Sub" with him and is not above talking about the mistakes and absurdities that cost many of his colleges their lives.

I've read all of the books listed, and value the sites that I have linked to. Don't mistake this as a comprehensive list, there is plenty more (and possibly better) out there.

Good Luck, and I hope you found this helpful!

Edited for formatting