Irony of Kitano
Kitano is the student's former teacher, and we would therefore expect him to have a duty of care towards the children. However, he is shown to be a deranged and violent character, killing some of the children for disobedience.
Irony of children
Children are generally thought of as being innocent and peaceful. However, in this film, we see that ironically some of the children are violent, brutal and psychopathic. This is especially true of Kazuo, who volunteers and kills many of the children.
Situational Irony
At the beginning of the film, the children think they are going on a field trip, and have no idea what is about to happen. However, they are then gassed and taken to an island and forced to take part in the "Battle Royale."
