Arnold leads teams for the smuggling group Headkeeper, noted for his operational responsibility and unwavering vigilance. He issues exact directives to members, showcasing dependable leadership under intense pressure. His key involvement starts with a mission to recover a Headkeeper package mistakenly shipped on a delivery truck. Discovering the driver, Innumael Grauer, was arrested for smuggling the package's weapons, Arnold orchestrates a prison break. He commands the operation to free Innumael and retrieve the package, triumphing against imperial security.

During the ensuing escape, Captain Helman's imperial soldiers ambush Arnold's team. Outnumbered and hindered by slower transport, they fight but are overwhelmed. Arnold engineers explosive diversions, enabling Headkeeper's evasion.

Later, Arnold joins a mission to rescue Headkeeper operative Elfriede, who infiltrated a shuttered mental institution probing organizational betrayal. With Benjamin, he finds Elfriede transformed into a monstrosity by unethical experiments. Unable to reverse her condition, they witness her death during a rampage.

Arnold collaborates closely with Headkeeper members like Schaake Gutheil during package retrievals and imperial evasion. His role persistently encompasses strategic planning and on-site command in pivotal operations.