Fen is a minor character in the series, appearing as a ghostly male spirit who resides in the kitchen of Uralis Castle. His background is rooted in tragedy, as he was killed during a violent siege on the castle. In life, he lived in the space above the kitchen ceiling, and after his death, he chose to remain there as a spirit, unable or unwilling to leave the place that was most familiar to him. His ghostly appearance is striking and memorable, defined by a shaved head and a sword lodged directly through his skull, a constant visual reminder of his violent demise during the castle's attack.

In terms of personality, Fen is subtle and unobtrusive due to his ghostly nature, but he is also characterized as curious, slightly mischievous, and observant. He seems to genuinely enjoy watching the bustle and activity of the castle kitchen, continuing to take an interest in culinary affairs from beyond the grave. He has a habit of being something of a tattletale or informant, as he takes pleasure in reporting on small dramas and secrets, such as the Queen of Uralis hiding broccoli in various dishes. This behavior suggests he finds entertainment in stirring up minor conflicts and revelations, using his unique position as an unseen observer to his advantage.

Fen is completely invisible to almost everyone in the castle, making him a secret observer whom only one person can perceive. His sole and most significant relationship is with Prince Bonchien Nicoli la Tasty Peach Uralis, who is the only character capable of seeing and communicating with him. This unique connection allows Fen to act as a hidden confidant and spy for the prince, whispering important or amusing information about kitchen mischief and other hidden activities to him. His role in the story is tightly bound to this dynamic, serving as Bonchien’s eyes and ears in places where the prince himself cannot be. By secretly informing Bonchien about the Queen's actions, Fen directly influences the small, interpersonal intrigues within the castle walls.

There is no available information about any significant development or change in Fen's character over the course of the narrative. His existence remains largely static, as he is a lingering spirit whose death has fixed him in a permanent state. Regarding his notable abilities, Fen's primary power is his ghostly nature, which grants him invisibility to the general population and apparently allows him to exist unseen within the castle's kitchen. However, his abilities are limited, as he cannot interact with the physical world in a direct way that most people would notice. His only effective "ability" is his selective visibility, as he is wholly undetectable to all except Bonchien, which enables him to gather and relay information without ever being discovered by others.