When stuck for anything better to say, we critics will occasionally argue that there’s “a better film struggling to get out” of some compromised entertainment or other. Never was this old saw more appropriate than this week.

The folks behind this mildly entertaining, competently mounted historical drama (a surprise hit in Japan) are making much of Tommy Lee Jones’s performance as Gen Douglas MacArthur. Though a little rounder than the great man, Jones confirms that he would be ideal casting for a MacArthur biopic.

Like a surprising number of the second World War generals – notably Montgomery and Patton – the conqueror of the Philippines was an eccentric with pronounced megalomaniac tendencies. Jones has great fun playing up MacArthur’s carefully maintained persona: he puffs the corn-cob pipe, he brandishes the aviator sunglasses, he stands as if constantly posing for a statue. Unfortunately, Tommy is barely in the blasted thing.

The actual focus of the film is on the lesser-known Gen Bonner Fellers who, while MacArthur was overseeing the occupation of Japan, carried out an investigation into the Emperor Hirohito’s culpability in the launch of the Pacific war. (The title of the film alludes, surely, to both Hirohito and MacArthur.)

Played by Matthew Fox with all his customary invisibility, Fellers plods around talking to various politicians and generals, always aware that, should the emperor avoid prosecution, he, rather than MacArthur, will take all the flack.

Some of the discussions are a bit on-the-nose: the argument that, after Hiroshima and Nagasaki, the US was in no position to take the moral high ground hardly needs to be stated explicitly. But Emperor offers a reasonably interesting and impressively lucid explanation of the legal process. Sadly, an unnecessary, hokey romantic subplot – too Madame Butterfly for words – keeps getting in the way.

Emperor will do well enough. But if you want a more nuanced take on the same events, check out Alexander Sokurov's extraordinary The Sun (2005).