The story opens with the sudden appearance of the shinigami, Rukia Kuchiki, in Ichigo Kurosaki's bedroom. She is surprised at his ability to see her, but their resulting conversation is interrupted by the appearance of a hollow, an evil spirit. After Rukia is severely wounded while trying to protect Ichigo, she intends to transfer half her powers to Ichigo, hoping to give him the opportunity to face the hollow on equal footing. Ichigo unintentionally absorbs almost all her powers instead, allowing him to defeat the hollow with ease.

The next day, Rukia appears in Ichigo's classroom as a transfer student. Much to his surprise, she appears to be a normal human. She theorizes that it was the unusual strength of Ichigo's spirit that caused him to absorb almost all her powers, thus leaving her stranded in the human world. Rukia has transferred herself into a gigai — an artificial human body — while waiting to recover her abilities. In the meantime, Ichigo must take over her job as a shinigami, battling hollows and guiding lost souls to Soul Society.