In this fantasy book series, each volume is dedicated to one element. The first volume is Earth (volume 2: Ore, volume 3: Air). The most important thing is the recognisability of the series, so the basic structure should also work for the other parts.
The typography should therefore emphasize the element in particular, write "EARTH" at the largest size.
The first book's main character is the earth walker Narna Feuervogel with her staff (the character will be replaced for volumes 2+3). Narna has red hair, pointed ears, freckles, and green eyes and wears a dress made of leaves.