Jane is a genetically modified soldier and love interest of John, serving in the Ghost Brigade. She is intelligent and skilled in combat, exploring her humanity through her relationship with John.

Harry is John's friend and a former physics teacher who joins the CDF for a new life and scientific curiosity. He provides scientific insights and raises questions about the Colonial Union's operations.

Viveros is John's first commanding officer in the CDF, originally from Peru. She is tactically savvy and offers John insight into the complexities of the CDF.

The Consu are an alien species and adversaries of the CDF, described as technologically advanced and motivated by religious beliefs. They engage in combat with humans as part of their own colonization efforts.