Diana Rubens is a character who appears in the anime Spice and Wolf II. She is introduced as a reclusive alchemist and town chronicler living in Kumerson, a city where she resides in a dim and unkempt home filled with stacks of dusty books. Due to her solitary lifestyle and her masculine-sounding first name, she is frequently mistaken for a man, an assumption that catches even the merchant Kraft Lawrence off guard when they first meet.

Beneath her human appearance, Diana is not an ordinary human at all. Holo, the Wise Wolf of Yoitsu, recognizes Diana as a kindred spirit: a pagan deity or animal spirit, whose true form is that of a giant white bird. This heritage grants her several supernatural abilities. She possesses immortality or an extremely long lifespan, having lived for centuries without visibly aging. This agelessness once forced her to leave a human lover, a traveling priest she had helped build a church for, when he grew suspicious because she never grew old. She can also transform, and while she is never shown changing shape in the story, her home, which is littered with large feathers, strongly implies that she can assume the form of a massive bird at will.

Personality-wise, Diana is initially presented as an enigmatic and perhaps intimidating figure due to her choice to live in the worst part of the city. However, she is ultimately a kind and insightful individual who takes a great interest in collecting stories and legends. She does not typically welcome visitors unless they know a specific pass-phrase, indicating a preference for a quiet and controlled existence. Despite her reclusive nature, she possesses a mischievous and playful side. During the pyrite speculation incident, she deliberately withholds information and sets up a situation that forces Lawrence and Holo to confront their true feelings for one another, effectively playing a prank on them to bring them closer together.

In the story, Diana serves as a crucial ally and catalyst for events in the Kumerson arc. Her two primary roles are as a source of information and as a key player in a complex economic scheme. Lawrence seeks her out in his quest to find the location of Holo's birthplace, Yoitsu. As the town chronicler, she provides him with the legend of Holo and the general location of the lost land. Later, she becomes the central figure in the speculative battle between Lawrence and his rival, Fermi Amati. For his plan to succeed against Amati, Lawrence needs to acquire a large quantity of pyrite, which Diana happens to possess. Through a deal she strikes with Holo before Lawrence even arrives, Diana arranges to sell the pyrite not to Lawrence, but to someone else, ultimately revealing that she had been acting with Holo to help resolve the couple's conflict.

Diana's relationship with the main characters is marked by a unique understanding, particularly with Holo. As two immortal beings, they share a rare connection and easily recognize each other's true natures. Diana treats the quarrel between Holo and Lawrence with the knowing perspective of someone who has experienced similar sorrows of loving a mortal. Her interactions with Lawrence are more direct and teasing; she answers his questions about the possibility of a pagan god and a human having children, and after their ordeal is over, she tells him to cheer up, subtly acknowledging his unspoken feelings for Holo. While her major role is fulfilled in the third story arc, Diana does not disappear from the narrative entirely and appears again in later material, where years afterwards she responds to an invitation from Holo and reflects on the events that transpired in Kumerson. Her most notable ability, apart from her supernatural longevity, is her deep knowledge of regional myths, folklore, and history, which is central to her work as a chronicler and allows her to aid Lawrence in his journey.