Berthold commands the palace guard in Aitheria, leading subordinates like Hans and Nikolaus. His formidable combat skills, forged in military service, earned him the moniker "The Devil," particularly after a wartime clash with an enemy knight bearing a squid emblem that deepened an existing aversion to seafood.

Raised in the mountains, Berthold married Hermina, whose coastal heritage contrasted sharply with his own, despite their age difference. Financial necessity initially led Hermina to work at the interdimensional izakaya Nobu, where Berthold became a regular. His early orders reflected his phobia, favoring items like whole pickled cucumbers and soy sauce-flavored chicken karaage.

Repeated exposure at Nobu spurred his character development. He gradually conquered his deep-seated fear of squid, beginning tentatively with grilled squid tentacles seasoned with shichimi chili powder mayonnaise. He progressed to ika soumen, shioka, ginger-braised squid, squid dumplings, squid rings, and pickled squid. His culinary journey expanded to include eel dishes such as unadon and umaki.

His professional duties intersected with Nobu during crises. He spearheaded efforts to protect the establishment from corruption when city council chairman Bachschouf attempted to seize it and annul his marriage, coordinating guards, guilds, and nobles to thwart the scheme. His diplomatic role emerged during visits by foreign delegations, such as safeguarding an Oirian princess and facilitating cultural exchanges through Nobu's cuisine.

Personal milestones include fathering twins. His evolving relationship with Hermina is reinforced by shared experiences at Nobu, where her seafood expertise complements his ongoing culinary adaptation, solidifying his integration into Aitheria as both a military leader and family man.

He is consistently depicted with brown hair, brown eyes, and facial hair, wearing the palace guard's standard attire.