I just watched Taegukgi. It was the 4th or 5th time I have seen it, but the first time on Blu-Ray. It is one of the truly great war films of our generation.
Did you buy it from Korea as I've not seen it sold in the US. Well this was a year or so ago when I was looking. It's been a while. But it should still work for you in Japan and us in the US due to the Region Codes being dropped to 3 instead of 5 like the DVD's were.
The Blu-ray Disc region coding scheme divides the world into 3 regions, labeled A, B, and C.
Region A includes most North, Central and South American and Southeast Asian countries plus Taiwan, Hong Kong, Japan and Korea.
Region B includes most European, African and southwest Asian countries plus Australia and New Zealand.
Region C contains the remaining central and south Asian countries, as well as China and Russia.
In attempts to circumvent region coding restrictions, stand-alone Blu-ray Disc players are sometimes modified by third parties to allow for playback of Blu-ray (and DVD) discs with any region code.[83] Instructions ('hacks') describing how to reset the Blu-ray region counter of some computer BD Disc player applications to make them multi-region indefinitely are also regularly posted to video-enthusiast websites and forums. Unlike DVD region codes, Blu-ray region codes are verified only by the player software, not by the drive and the computer operating system. The code is stored in a file of the player program or in the registry. In stand-alone players, it is part of the firmware.