Not arrange national holidays, parades and celebrations of the end of the war with Japan
China may hold war parade at Marco Polo bridge, site of first conflict with Japan | South China Morning Post
Japan has apologised many times, given war reparations. Since the end of the WWII it has been an integrated global player.
There is a worrying trend in the last few years that they are starting to beat the nationalist drum in Japan but in comparison to China or many nations it really is not that worrisome. The checks and balances in the governmental society helps ensure a radical nationalist leader can't stay in power. There are no purges of political enemies, tightening of press, closure of free internet, massive build-up of arms and angry rhetoric to it neighbours.
But its pacifist constitution probably does need to be revised to allow it a role in ensuring peace in East Asia.
In Europe when such ceremonies are held Germany & Italy are obviously invited.