Ludwig Herzog von Mohn nahe Liechtenstein bears the noble title of Herzog, or Duke, ranking second among Kuchen's aristocracy. His mother is the king's sister, making the king his uncle, while his paternal uncle fathered Camus, establishing Ludwig and Camus as cousins. Ludwig's father also holds the dukedom. He has a younger sister and brother, with household affairs managed by two housekeepers, Augusta and Clemence. Ludwig is left-handed.

He presents a cold, aloof demeanor tinged with arrogance, maintaining calculated indifference toward societal expectations tied to his rank. Though emotionally detached, his blunt remarks unsettle others. Despite this exterior, he exhibits sharp perceptiveness regarding character and emotions, offering precise guidance to those he values. He welcomes fair challenges and openly acknowledges his own emotional distance, contrasting himself with idealists like Orpherus—a perspective others criticize as potentially dangerous.

Ludwig shares an exceptionally close bond with Naoji, whom peers dub his "shadow." Ludwig sustains this proximity, described as keeping Naoji "as close as a nightingale in a cage." During their final year at Rosenstolz Academy, Ludwig faces severe treason accusations, forcing him into hiding while friends work to clear his name. Rumors circulate about a potential engagement to Charlene Hartvich, with peers viewing him as a highly desirable marital prospect due to his status, though the engagement remains unconfirmed.