Dangers of Totalitarianism
The main theme of the film is the danger of a totalitarian regime - or any kind of political dictatorship. The government does not tolerate any form of what they view as disobedience, which is basically any kind of expression of disagreement with them. However, there is increasing dissent amongst the youth of the nation, and the government wants to nip this in the bud quickly, whilst at the same time saving themselves the expense and the possible loss to the military of suppressing what is viewed as a potential insurgency. That is why the Battle is created.
The Battle requires complete obedience to the government. By kidnapping the students and taking them to an island rather than on a field trip, as their parents were informed, they have demonstrated that they feel they have more rights to the kids than their parents do. Participation in the Battle is non-negotiable. Even play acting participation is punishable by death. The fact that Kitano shoots anyone trying to get out of playing even before the game has started shows the complete disregard that a regime like this has for human life, and the fact that they will stop at nothing in order to maintain control.
Loyalty
Despite the fact that they are almost forced to kill or be killed, some of the students manage to maintain a loyalty to each other that actually puts their own lives at risk. This is a testament to the strength of character of some of the participants in the battle and it also shows that it is possible to stay true to oneself even in the most appalling and life-threatening of circumstances. Shuya is loyal to his best friend, Yoshitoki, and even after his friend's murder shows his loyalty by protecting Yoshitoki's girlfriend, Noriko. Similarly when an alliance is made between Shuya and Kiwada, both remain loyal to it, even if it means that Kiwada sacrifices himself at the end.
Courage
The students who are playing the game with a view to making sure that as many of them survive as possible exhibit an enormous amount of courage, because they know that doing anything other than visibly trying to murder each other could result in their own death. The class representative, for example,shows real leadership by setting up a makeshift hospital in the lighthouse, and Kiwada shows his courage by trying to hack into the system and derail the game all together.
