Considering Japan's only in the past few decades gotten more honest about it's war crimes, it's not shocking that Korea (and a lot of the rest of Asia,) is taking it's sweet time about getting over it. That's the kind of thing that's going to take generations to iron out. Considering it's 20-somethings and younger in Japan who tend to admit to Japan's war atrocities, it'll be another generation before South Korea (and China, and so on,) begin to get over them. The people who suffered under that regime have to all be in the ground, and so do their children probably.
Think of it in terms of slavery in the US - there is no one alive today who is was on either side of slavery, but the on-going issues in it wake have left a scar that still is left unhealed in someways. Japan's actions during World War 2 may take just as long to heal, especially since they have lack Germany's vigilance in keeping nationalism in check.
I mean, Japan is still an intensely xenophobic country in a lot of ways, and perhaps the only reason any sense of multi-culturalism has crept into anime and manga (outside of a generation of much more broad-minded manga-ka) is because Japan is enamored of western pop culture and because the insanely low birth rates have forced Japan's hanRAB in regarRAB to issuing visas to foreigners who want to work there, changing the cultural and ethnic make up of Japan. Take America's problems with people not wanting to do dirty jobs, then compound that with the birthrate being below replacement levels, and guess what: you have a lot of non-Japanese suddenly in the mix, and not just as Jet teachers. Characters like Chad in Bleach are based off of a very real trend in Japan.
Still, it'll take years of a multi-cultural Japan for the rest of Asia's view of the country to change on it I think, and it will take the old hardline xenophobes (too many of whom still hold seats in the Diet,) to die off for things to really change. It's what it's taken for things to change in the US, and we've had the advantage of heavier, immensely diverse immigration, active protesting and higher birth-rates marginalizing those narrow attitudes faster. The west has been active with being progressive - Asia in general has at points been somewhat slow (and not just on racism and honesty in history, but also on sexism, homosexuality and just about every other social issue you can dream up.)
And now I've made a whole bunch of generalizations too.