Literally every country that was ever colonized by Japan hates them in ways that are impossible to convey to most westerners. Same dynamic with China too. This is why the people of Vietnam LOVE Americans despite our war with them (their war vs China is the "1000 years war")

Most of the people from the countries that Japan colonized openly want/beg for westerns colonialists to "come back".

American WASPs and Burmese people (among many others) both have a history of their grand/great grandfathers being brutally tortured circa WW2 by the average Japanese persons great grandfather.

As it turns out, a slur that's literally just removing a couple letters from your countries name isn't all that bad in the grand scheme of things. I'll stop using it when they stop calling me "Jingai" and "Gaijin" because I had the audacity to put my seat down on the Shinkansen without asking the entire train if I was going to lose face by doing it.