I was snooping around on the web when I found some videos about the upcoming Bleach movie, Goodbye Rukia. One youtube video I found has a synopsis and some screen shots. Here is the plot summary I found on this unreliable source, choose to believe it if you want.
***SPOILER***
Some villain carrying a sickle sneaks into Mayuri's lab and attacks him. Mayuri flips out and uncontrollably hits his control panels releasing a cloud of Reishi over Seiretei. Kenpachi rushes into Mayuri's lab to see what's going on but there is a huge explosion of Reishi that messes up Seiretai. Rukia, who is watching the event from afar is attacked by the sickle guy and he steals her "heart". Ichigo senses something amiss and goes to Urahara who tells him that Seiretei has been "destroyed". Ichigo ventures off to soul society with Kon but when they get there it's trouble. The catastrophe has caused all the shinigami to lose their memories and when Ichigo arrives they receive him as an enemy. He is forced to use Vizard form and the shinigami conclude he must be the culprit. Since Rukia was also not in Seiretei when it happened the shinigami have forgotten her as well. That's where the synopsis leaves off.
Here is where I got it from:
http://www.youtube.com/watch?v=Q4o6igCLX5Y&feature=relatedthough it was from a youtube video the synopsis seems believable. If this is the plot I can't wait to see the movie.