Windom, also called Windam, stands as one of three legendary Rune Gods protecting Cephiro. This ancient mecha acts as the designated combat partner and primary weapon system for Fuu Hououji against threats to Cephiro's stability.

Initially manifesting as a giant green bird with four wings, Windom resides within a floating crystal mountain shrine before activation. Upon full summoning, its form shifts into a humanoid mechanical configuration ready for combat. Its revival differs between continuities: in the anime, Fuu must choose between gaining Windom's power or saving Ferio from the anime-exclusive antagonist Inouva; her decision to rescue Ferio unexpectedly enables Windom's activation. Conversely, the manga depicts Windam's revival occurring solely through Fuu's unwavering determination.

Windom participates in critical battles across both narratives. It fights alongside fellow Rune Gods Rayearth and Celes during the conflict against High Priest Zagato. Following Zagato's defeat and the collapse of Cephiro's Pillar system, Windom deactivates when the Magic Knights return to Earth. Reactivated during Cephiro's later invasion crisis, it combats forces from Autozam, Chizeta, and Fahren. Windom contributes to defensive operations against Lady Debonair and Nova, supporting the Knights' efforts to stabilize Cephiro by establishing a new societal structure.

Synchronizing with Fuu, Windom unleashes specialized attacks including "Wings of Green" (defensive augmentation), "Force of Green" (allied recovery), "Light of Green" (statistical enhancement), and "Wind of Mashin" (sword-based offensive maneuvers). These abilities primarily manifest during Rune God deployment sequences.

The name originates from automotive branding conventions consistent across the series, specifically referencing the Toyota Windom vehicle platform.