Mare Selen el Phiriazar serves as a prince of the religious nation of Selenfalen and is the younger brother of fellow prince Ruze Selen el Phiriazar. Exhibiting a deeply reclusive and introverted nature, Mare possesses a pronounced aversion to sunlight, consistently seeking darkened environments. This compels him to avoid outdoor excursions and social engagements, often retreating into enclosed spaces like chests during travel to evade light exposure. His withdrawn demeanor initially presents as dismissiveness toward others, including Ani Inako, princess of Inako. Mare demonstrates keen intelligence within his specialized interests, aligning with his portrayal as an otaku prince devoted to niche hobbies and solitary pursuits.

Gradually across the narrative, Mare emerges from self-imposed isolation. He incrementally engages more with his surroundings, particularly Ani, reflecting growing comfort with social exposure and willingness to join group activities. His initial indifference toward Ani shifts into a genuine bond, culminating in romantic interest by the story's conclusion. This evolution signifies meaningful change while preserving core aspects of his personality.

Mare's relationship with Ruze exists within Selenfalen's royal family dynamics and political context. Ruze maintains greater public visibility yet operates under heavy advisory influence, contrasting with Mare's initial seclusion within their princely roles. Mare's presence contributes to group dynamics among princes of three nations, his evolving interactions mirroring broader themes of alliance-building and overcoming differences. His development remains consistent with foundational traits, reflecting adaptation rather than complete transformation.