The show was first revealed to the public in a teaser reel at Comic-Con 2004, and started show the episodes from 21 February 2005. In the United States, first two episodes of the series were shown together in a one-hour premiere event. A second twenty-episode season ran from 17 March 2006 through 1 December. A third and final season, beginning September 21, 2007, featured twenty-one episodes rather than the usual twenty. The final four episodes were packaged as a two-hour movie.