Bleach: Memories of Nobody (2006)

In Karakura Town, unidentifiable spirits begin appearing en mases. While attempting to deal with these strange souls, Ichigo Kurosaki and Rukia Kuchiki meet Senna, a mysterious shinigami who wipes out most of them. Senna refuses to answer any questions, so Ichigo is forced to follow her while Rukia tries to find out what's going on.