"Sweet Valerian" is a fantasy romance anime set in a world where humans coexist with magical beings known as Valerians, who possess unique abilities tied to nature and emotions. The narrative centers on Liora, a young herbalist living in a secluded village, and Kael, a Valerian with the power to manipulate memories. Their paths cross when Kael, injured and pursued by a rogue faction of Valerians seeking to exploit his abilities, stumbles into Liora's care. Despite initial mistrust, Liora decides to help Kael, setting off a journey that intertwines their fates.

As the story progresses, Liora and Kael uncover a conspiracy threatening the fragile balance between humans and Valerians. The rogue faction, led by the enigmatic and power-hungry Valerian named Eryndor, aims to harness Kael's memory-altering powers to rewrite history and dominate both races. Liora's knowledge of ancient herbs and her growing bond with Kael become crucial in countering Eryndor's plans. Along the way, they are joined by a diverse group of allies, including a human knight named Ryn, who harbors a deep-seated grudge against Valerians, and Sariel, a Valerian healer struggling with her own conflicted loyalties.

The narrative explores themes of trust, identity, and the consequences of wielding power, as Liora and Kael navigate their evolving relationship amidst escalating tensions. Flashbacks reveal Kael's tragic past, including his separation from his sister, who was captured by Eryndor's faction and used as leverage to control him. Liora's determination to protect both humans and Valerians drives her to confront her own fears and limitations, while Kael grapples with the ethical implications of his abilities and the weight of his past actions.

The climax of the series sees Liora and Kael confronting Eryndor in a battle that tests their resolve and the strength of their bond. The resolution hinges on Kael's decision to sacrifice his powers to sever Eryndor's control over the Valerians, restoring peace at great personal cost. The story concludes with Liora and Kael parting ways, each carrying the lessons of their journey into an uncertain future, leaving the door open for potential reconciliation and growth. The series balances its fantastical elements with intimate character-driven moments, creating a narrative that is both expansive and deeply personal.