Yeah a lot of people might not be aware just how heinous Japans actions were in The Second Sino-Japanese War (the Chinese War of Resistance) in the lead-up to Asias involvement in WWII.
I think that's probably true - Japan has such a sanitized reputation now (which, frankly, isn't entirely deserved), and most people probably don't ever take a history class after high school, so a lot of people probably genuinely don't know how bad it was. I did a little over 3 years of an undergrad history major and never heard a word about it. The only reason I know anything about it is because my AP US History teacher in high school told a few of us about it after a class on WWII. I had nightmares about some of the pictures for a few nights. I see why they don't generally teach it to kids.
The funny thing about John Rabe is that he was probably the only Nazi in any sort of power after The Night of the Long Knives to think they were still a socialist party, because he was off chilling in China and everyone forgot about him.
The swastika predates Nazi Germany, but is forever tarnished by it. In Asia, the flag of Imperial Japan is often seen as a symbol of fascism, Imperialism, and war crimes.
More power to them for trying to reclaim it! It was stolen anyways.
The difference with Imperial Japan is that the flag is still being used by the same group that committed war crimes. The Rising Sun can't simply be reclaimed, unlike the Swastika.
Point being is that there's a reasonable reason for the Japanese Naval flag to be in a Japanese Naval meme. If you want at reason to think the meme wasn't made in good faith, I'd be more worried about how the Japanese guy is holding a machete to the other guy's throat. That actually does conjure up ideas about WWII war crimes.