With the utmost respect for those who suffered at the hands of Japanese, does the current population / government /monarchy of Japan have a duty to apologise? Some of those Japanese old boys guilty of lesser offences have apologised. The nation, no. Maybe it isn't part of their culture and, there are very few Japanese left with 'living memory'. Furthermore, they got two buckets of instant sunshine in short order and that evens things up (not that that was the idea).
As for teaching Japanese history, warts and all, I can see why it is thought necessary by some in the West. Equally, the Japanese- 'culturally' - may rather forget/pretend Manchuria/WWII didn't happen. Making allowances for cultural sensitivities/differences is a 21st Century hot topic. (Devils' advocate hat on here).
We all wail when the notion of UK PLC apologising for slavery or the Irish potato famine :roll: is mentioned. Apologising in the immediate aftermath may be appropriate, 2-3 generations (or more) later is empty and unnecessary.
Has Italy ever apologised for Rome's conquest?