 In the movie, the blade Motoko uses is not her usual polished steel  Katana, but instead a very dark colored blade. Closer inspection of  the swords hilt reveals it is the Cursed Blade of Hina from the  previously unreleased 25th Episode of the Love Hina TV series (this  episode can now be found on the Love Hina Christmas Movie DVD). In  Episode 25, it is revealed that her blade was broken in a duel with  her older sister, but Keitaro gives her the cursed blade. Assumedly,  Motoko kept the sword as her own since it appears in the movie.