Felix Arc Ridill is a central character in the anime Secrets of the Silent Witch, known for his dual identity as both the second prince of the Ridill Kingdom and the president of the student council at Serendia Academy. At first glance, he appears to be an impeccably accomplished young man who excels in both his academic pursuits and diplomatic duties, carrying himself with a composure and talent that draws widespread admiration. His physical appearance is notably harmonious, described as adhering so closely to the golden ratio that his features are considered strikingly attractive. He has honey-blond hair and blue-green eyes, and to the public, he embodies the image of a perfect prince and an ideal candidate for the future king.

Underneath this flawless exterior, Felix harbors several layers of secrecy and hidden motivations. Officially, he is the person that the protagonist, Monica Everett, has been assigned to protect, though he is unaware of her mission at first. While he pretends to have no interest in magic, he is in truth a devoted secret fan of the Silent Witch, the legendary mage whose identity Monica conceals. This hidden fascination contrasts sharply with his public persona. In his role as a prince, he is known to be nice to those around him but can be cold to anyone who offends him, and he is careful to maintain a certain distance from those trying to gain his trust, largely due to past assassination attempts and a deep-seated wish for freedom. He also enjoys teasing Monica, finding amusement in her often flustered reactions.

The most significant revelation about Felix Arc Ridill is that this persona is a constructed identity. The real second prince, a frail and kind-hearted boy named Felix, died in a tragic accident several years before the story begins. The character known as Felix is actually an imposter, his former attendant and best friend, Isaac Walker. Following the prince's death, Duke Clockford, Felix's maternal grandfather, forced Isaac to assume the prince's identity to conceal the loss and to have a puppet ruler for his sinister political schemes. As Isaac, and when hiding his true self under the alias Ike in the pleasure district, he is much more relaxed, friendly, and genuine. His core motivation then becomes twofold: to survive as the imposter prince while secretly working against the Duke's control, as he notably does not want Duke Clockford to intervene in his affairs. He also feels a powerful, instinctive need to protect and care for others, a trait he exhibited towards the real prince and which later extends to Monica when they meet at the academy.

His key relationships are defined by these secrets. His bond with Monica Everett is central, as he is her charge, and she is the mage he secretly admires, creating a complex dynamic of hidden identities. His relationship with his grandfather, Duke Clockford, is one of manipulation and resistance, as he is the Duke's unwilling pawn. His past with Elliott Howard, another noble, is complicated, as despite Elliott having wounded him, the real Felix had forgiven him, a memory that likely weighs on the imposter. The character undergoes significant development as he navigates this treacherous double life, balancing the expectations of a prince with the search for his own identity and freedom. He possesses notable abilities beyond his scholarly and political talents. He is proficient in maintaining his deep cover, has a keen situational awareness that allows him to sense when he is being watched, and has a peculiar affinity for crawling animals like snakes and lizards.