Feff commands as a major Mardook military leader, his loyalty initially absolute to Emperor Ingues. He actively enforces the Mardook culture of destruction despite harboring personal doubts. These doubts intensify after interacting with Ishtar, the Emulator used to control Zentradi warriors through song. Initially viewing Ishtar as a mere tool, his perspective shifts, compelling him to treat her differently. He exerts significant effort to retrieve her, demonstrating a deepening personal investment.

His direct military command utilizes advanced combat technology. He pilots the customized Gigamesh Type II (Gilgamesh Mk II), a heavily armored yet highly maneuverable Mardook Commander Combat Mecha. This suit excels at close and medium range, equipped with retractable anti-armor battle claws, blades, powerful wing cutters on extendable arms, and missile launchers carrying 100 mini-missiles. Advanced systems include radar, targeting computers, electronic countermeasures, and trans-atmospheric flight capability, reflecting his rank.

Feff's development centers on his evolving relationship with Ishtar and wavering commitment to Mardook ideology. His burgeoning feelings for her directly challenge his loyalty to Ingues and the destructive Mardook principles. This culminates in a decisive betrayal: he abandons the Mardook cause, performing a Heel Face Turn to side against Emperor Ingues, positioning him against his former leadership.

Within the narrative's interpersonal dynamics, Feff becomes part of an emotional conflict. His feelings for Ishtar contribute to a love triangle involving her and the human reporter Hibiki Kanzaki, further complicating his loyalties. He ultimately survives the conflict, having rejected the Mardook's path of destruction.