"xxxHOLiC: Rei" is a continuation of the original "xxxHOLiC" series, written and illustrated by CLAMP. The story resumes with Kimihiro Watanuki, a high school student who possesses the ability to see spirits and supernatural entities, working at Yūko Ichihara's mysterious wish-granting shop. Yūko, a powerful witch, had disappeared at the end of the original series, leaving Watanuki to manage the shop in her absence. Despite her disappearance, her presence lingers, and Watanuki remains deeply connected to her and the shop's operations.

The narrative explores Watanuki's ongoing struggles with his spiritual abilities and his commitment to fulfilling the wishes of those who seek the shop's help. Each chapter typically revolves around a new client whose desires or problems are intertwined with the supernatural. Watanuki, alongside his companions—the enigmatic Domeki, who shares a complex bond with him, and the twin spirits Maru and Moro—navigates these cases, often uncovering deeper truths about human desires, regrets, and the consequences of meddling with the supernatural.

A significant subplot involves Watanuki's internal conflict and his longing for Yūko's return. His dedication to preserving the shop and its legacy reflects his growth from a reluctant participant in the supernatural world to a responsible caretaker. Domeki, who possesses his own spiritual powers, continues to play a crucial role, both as a protector and as someone tied to Watanuki's fate through a shared past. Their relationship evolves, marked by moments of tension and mutual understanding.

The series maintains a balance between episodic storytelling and an overarching narrative, delving into themes of fate, sacrifice, and the blurred boundaries between the human and spiritual realms. The tone often shifts between melancholy and whimsical, reflecting the duality of the characters' experiences. As the story progresses, Watanuki's journey becomes increasingly intertwined with the mysteries of the shop and the lingering influence of Yūko, culminating in revelations about their intertwined destinies.

"xxxHOLiC: Rei" expands on the original series' foundation, offering deeper insights into its characters and their connections while continuing to explore the consequences of wishes and the price of supernatural intervention. The series remains a compelling blend of the eerie and the emotional, anchored by its rich character dynamics and intricate storytelling.