From WWE.com:

WWE and Tajiri have reached an agreement on his release. Monday Night RAW in Boston on Dec. 12, 2005, will be Tajiri s final appearance. Tajiri has decided to go back to his native Japan to work on writing a book. In addition, Tajiri plans to write news columns upon his return. WWE wishes Tajiri the best in all his future endeavors.

NOTE: As we noted here before, Tajiri had wanted to spend more time with his wife. More as we get it.