Hoo boy. There are a whole shitload of cultural issues with war guilt and WWII in general in Japanese society, enough to fill several books (which have been written).
But, long story short, the ruling party up until recently (Liberal Democratic Party, which was pretty much anything but), both through official statements and through the textbooks for schools, had a tendency to enforce what was called the Chrysanthemum Taboo (basically, you do not talk shit about the Emperor or we have our crazy right-wingers kill you), and just not talk about the war and gloss over war guilt.
And yeah, a manga of Mein Kampf is pretty... interesting, given Japan's involvement in WWII and their alliance.