Lord Feff commands as a major leader within the Mardook military. He spearheads the invasion of Earth, personally leading scout fleets against human defenses, demonstrating significant and ferocious combat prowess.

Initial unwavering loyalty to Emperor Ingues compels Feff to enforce Mardook's destructive culture, despite harboring private doubts about its extreme enforcement of purity. His perspective shifts during interactions with Ishtar, the Emulator assigned to his forces. Initially viewing her only as a tool to enhance warrior aggression through song, his attitude changes.

Exposure to Ishtar's Earth experiences and her embrace of human culture catalyzes Feff's development. He begins treating her differently, actively working to return her to the Mardook side. This evolves into personal feelings, culminating in Feff confessing his love for Ishtar as an individual, distinct from her role as an Emulator. His protective instincts drive him to attempt her rescue after her warship's destruction.

Feff's wavering allegiance culminates in direct opposition to Emperor Ingues. Understanding Ishtar's goal of promoting peace through Earth's culture and songs, he betrays the Mardook leader. This stems from his rejection of Ingues's genocidal policies and his desire to support Ishtar's vision. His actions prioritize her safety and objectives above his duty to the Mardook Empire.