The interactions and relationships of the Kaul siblings influence the actions of No Peak throughout its battle with Mountain. Despite disagreements and grudges, as the clan conflict worsens, they draw closer together, striving for a stronger relationship.

The notion that siblings, no matter how strong their bonds, struggle with personal tension is integral to Kekon culture. Deitist religion believes that human progress is irreversibly tied to sibling relations:

All earthly conflict, so the Deitist philosophers say, stems from the original offense of the children against their parents and of siblings against one another. All human progress and virtuous striving is like-wise an attempt to achieve familial forgiveness and a return to the spiritually and physically divine state (151).

Siblings fight, hold jealousies, and provoke each other at opportune moments, but these petty feuds often pale in comparison to their strong love for each other—a dynamic most apparent with Hilo and Shae, whose relationship fundamentally shifts in the face of family tragedy and clan crisis.

Shae and Hilo, who grow up in the shadow of their older brother Lan, are lifelong rivals. The two are close in age, so they attend school together, where they compete for academic and social success.