Mernes, a half-human, half-demon hybrid, serves as one of the Four Heavenly Kings in Demon Queen Echidna's army, bearing the title Shadowless General. His distinctive appearance includes white hair with bangs covering his right eye, piercing blue eyes, and a habitual long green cloak that partially obscures his face.

Sold into child slavery at a young age, Mernes endured a harsh upbringing before being acquired by the Assassin's Guild. There, he mastered exceptional espionage and combat skills, rising to become the guild's master by age sixteen. This traumatic past fueled profound resentment toward humanity, driving him to sabotage human defenses during Echidna's initial invasion. His original intent in joining her forces was to manipulate or seize control of the army for personal vengeance.

Personally, Mernes presents as calm, quiet, and serious, possessing high intelligence but severe communication difficulties. He rarely displays visible emotion and struggles significantly with social interactions, often relying on others to speak for him. Within the Demon Army, his strategic and covert capabilities are utilized in espionage, patrolling, and leading construction teams.

A pivotal shift occurs through interactions with Leo Demonheart. During a mock interview exercise, Mernes shares his painful background, prompting reciprocal trust from Leo. Hearing Leo's perspective on humanity's potential challenges Mernes's monolithic hatred, catalyzing a shift in his worldview. This exchange also fosters growth in his interpersonal skills, enabling him to engage more openly and actively listen.

His relationships with Echidna and fellow generals Shutina, Lily, and Edvard remain professional, though specifics are less detailed. Mernes's journey focuses on reconciling his traumatic past with newfound purpose within the Demon Army, gradually moving from isolation toward tentative integration.