"Earl and Fairy" is a fantasy romance anime set in 19th-century England, blending elements of folklore, mystery, and the supernatural. The story centers on Lydia Carlton, a young woman with the rare ability to see and communicate with fairies, earning her the title of "fairy doctor." Her life takes a dramatic turn when she encounters Edgar J.C. Ashenbert, a self-proclaimed earl who claims to be descended from the Blue Knight Earl, a legendary figure said to have been granted authority over the fairy realm by the fairy queen. Edgar seeks Lydia's expertise to locate a precious heirloom, the Merrow's Sword, which is tied to his heritage and the key to proving his noble lineage.

As Lydia becomes entangled in Edgar's quest, she discovers that his past is shrouded in darkness. Edgar was once enslaved by a criminal organization known as the Prince, and he seeks to reclaim his identity and freedom by securing the sword. However, his charming demeanor often masks his manipulative tendencies, creating a complex dynamic between him and Lydia. Despite her initial reluctance, Lydia is drawn into Edgar's world, where she must navigate a web of intrigue, betrayal, and danger.

The narrative unfolds as Lydia and Edgar face various adversaries, including members of the Prince organization and rival claimants to the Blue Knight Earl's legacy. Along the way, Lydia's knowledge of fairy lore proves invaluable, as many of the challenges they encounter are rooted in the supernatural. The series explores themes of trust, identity, and the clash between human ambition and the mystical world of fairies. Supporting characters, such as Edgar's loyal servant Raven and the mischievous fairy Nico, add depth to the story, providing both assistance and comic relief.

The plot is driven by a mix of episodic adventures and an overarching mystery surrounding Edgar's true intentions and the significance of the Merrow's Sword. As Lydia and Edgar grow closer, their relationship evolves from one of mutual distrust to a deeper connection, though Edgar's enigmatic nature keeps Lydia questioning his motives. The series balances its romantic undertones with action and suspense, creating a compelling narrative that appeals to fans of both fantasy and historical fiction.