Laplace is a major supporting character in the series, serving as the vice-chairman of the Moderate Harlequin Alliance, also known as the Moderate Clown Troupe. He is a powerful undead jester-class monster, often referred to as a demon, who appears disguised in clown-like attire consisting of a black mask, a hat with rabbit ears, and striped clothing. His true form is that of a rare Deathman brought into existence by Kagali, and his concealed identity is that of the former hero Sarion Grimwald, who has lost most of his memories.

Laplace presents himself as a laid-back, humorous individual who speaks in a Kansai dialect and constantly jokes, lies, and toys with others. This playful, easygoing demeanor makes others naturally distrustful of him, even when he is being sincere. However, beneath this clownish exterior, he is exceptionally cunning, strong, and manipulative. He cares deeply about his friends and family, prioritizing their well-being above all else. Despite his association with antagonists, he is not driven by a desire for world domination; rather, his primary motivation is to support his comrades in the Moderate Harlequin Alliance and to have fun alongside them. He is fiercely loyal to Kagali, the group's leader, and to Clayman, whom he considers a close friend.

In the story, Laplace first appears in the first season as a mysterious figure plotting alongside Clayman. He later works behind the scenes, inciting rebellions and infiltrating enemy territory, such as when he instigates Gabil to revolt or spies on the Holy Empire of Ruberios. Although he initially avoids direct combat, he demonstrates terrifying strength when provoked. In a notable confrontation, he kills Roy Valentine, a vampire of demon lord-level power, in an instant after learning of Clayman's death and enduring Roy's insults. He also shows a softer side by deliberately speaking mockingly of Clayman when informing the other clowns of his death, taking on the role of the villain to spare them from grief.

Laplace's key relationships include his unwavering loyalty to Kagali and his bond with Clayman, whose death deeply affects him. He also follows Yuuki Kagurazaka, though he does not share Yuuki's ambition for conquest. His interactions with the other members of the Moderate Harlequin Alliance—Tia and Footman—are marked by camaraderie, though tensions occasionally surface. Toward Rimuru Tempest and his nation, Laplace acts as an enemy due to his allegiance, but his hostility is more circumstantial than personal.

Over the course of the series, Laplace develops from a seemingly frivolous trickster into a complex figure who grapples with loss and demonstrates genuine kindness. His loyalty remains steadfast, and his hidden strength becomes increasingly apparent. His unique skill, Trickster (also referred to as Deceiver), prevents enemies from recognizing him, allowing him to feign death and escape dangerous situations—a tool he uses for infiltration and survival. He is considered the most formidable combatant within the Moderate Harlequin Alliance, possessing strength and intelligence that rival demon lords, though he often holds back his true power.