Unpredictability
Unpredictability is a central, recurring part of Mark's life. One day he is on the subtrans, and the next moment, sun flares strike–he and Trina are thrown into flux. At the start of the story, Mark has no idea what will occur that day. He can only hope for the best. When things happen, Mark and his friends have to adapt, adjust, and act accordingly. The unpredictability of the human world means that anything can happen to the ones he loves, and Mark must be ready to take unprecedented actions accordingly.
Fate
Tied along with unpredictability is the idea of fate, or the way things were always intended to occur. For example, Mark had always had a crush on Trina, but was never able to really able to make her view him in the same way. However, with the onset of the flares, Mark sometimes wonders if they are only together because everyone else they know is dead. Regardless, fate continues to bring them together.
Gender Roles
The idea of gender roles is relevant in The Kill Order. Mark and Alec spend a lot of time together; as they undertake a lot of physical action, and protect their female friends quite a lot. Not only are they the ones "pursuing" the women throughout the story, but they are also pursuing them to rescue them. At the same time that The Kill Order confuses gender roles, it also sees its characters conform to traditional conceptions of gender roles.
Masculinity
Tied in closely with the idea of gender roles is the concept of what masculinity is. Throughout the story, Mark always tries to braver, and he does in fact become a braver individual. He is able to become more courageous because of his love for his friends and for Trina. Mark learns a lot from Alec, following much of the old soldier's ways. At the same time, the old soldier Alec also learns from the youthful Mark. They teach each other, occasionally talk about women, and take their roles as the guardians–as "men"–very seriously.
Human Morality
Morality and ethics are central to the messages in The Kill Order. The first day of the story, government officials shoot poisoned darts at its remaining "citizens." This is not moral, and yet the people who committed the atrocity have their own reasons for doing so. Furthermore, there are several mercy killings in the story: friends are forced to put their friends out of misery, so that they will not keep suffering. The question of killing people is brought out into the light, and what role morality has to play in that. Mark constantly asks himself what is right and what is permissible in this mess of a world.
Desperation
Desperation and survival are central to the movements of the characters in this story. The instinct to survive is what drives Mark and his friends onward; they rely on each other and live for each other. They know they must survive in order to help each other, and hopefully one day the world will give them the purpose to keep living. However, after the Berg strikes with poison darts the first time, desperation as a central theme becomes even more important. Now the friends are not just surviving day-to-day and living day-to-day, but they must actively understand how to fight off the dangers of the world to continue existing.
Normalness
Mark and his friends want things to return to normal. Although they understand that things cannot return to how they were before the sun flares, there is a desire to stop living like animals, and to have a stable environment where day-to-day survival is not the top concern. After the Flare strikes, the idea of normality is even more important. People now are openly not normal, as they are becoming insane. The story thus questions if there ever really is a "state of normality" in the first place.
