The Greeks used the theme of purification through suffering. It is, I believe, the central them of The Iliad. Kaji is a classic hero. He is a man of stuff that few are. In the first, he is nearly destroyed by his own ethical being. Seen as an enemy sympathizer (mainly the Chinese) he ignores the platitudes of war and sees it as something humanity doesn't need. Of course, mankind only knows war and makes heroes out of warriors (even if they must die) and glorifies the whole idea of war. In the second part of the trilogy, Kaji has been drafted and is seen as trouble and watched. He is put in charge of a group of mature soldiers (Japan is losing the war and calling middle aged men to fight). He tries to get his superiors to treat recruits with kindness. This really rubs the other soldiers the wrong way and he continues to be a liability to them.
In the latter part of the film, he and his men go into battle. Unfortunately, with the Japanese on the skids, they are attacked by a Russian tank battalion. They are sitting ducks. Kaji continues to exhibit his heroism, even though many of the men have lost their discipline. Yet instead of seeing himself as a hero, he continues to see the evils of war.