Nunca é explicado, mas todos os detalhes sobre a espada indicam que não foi .
O-Ren Ishii últimas palavras:
O-Ren utters with her dying breath "That really was a Hattori Hanzo sword", having been close enough to both see the symbol of Hattori Hanzo and feel the blade.
Por suas últimas palavras e como ela parecia surpresa, podemos acreditar que sua própria espada não foi feita por Hattori Hanzo.
E tomando o comentário de @ Walt como outra possibilidade:
In any case, as the comments there correctly assert, there's no emblem on it, and even if it was a Hanzo sword, it was certainly not made for her because she's way too young. She's about 29 in this movie and Hanzo stopped making swords 28 years ago, when she was 1.
Um pouco mais de informação sobre a espada e quando O-Ren a usou:
O-Ren's sword was only seen being used twice. First time was during the Yakuza bosses council meeting where O-Ren is seen decapitating Boss Tanaka for bring up her Chinese and American heritage as a negative. The second and last time, is when she and Beatrix Kiddo fight with both of their swords. The lack of a hand guard (tsuba) or handle wrapping classifies this sword as aikuchi (匕首?) (literally "fitting mouth"). Aikuchi is a form of mounting for small Japanese swords in which the handle and the scabbard meet without a guard (tsuba) in between. Aikuchi is style of sword mounting that is popular with Japanese nobility, perhaphs signifying O-Ren's status as Queen of the undeworld in Japan. Her particular sword is notable due to the sakura (cherry blossom) design on the handle (tsuka).
Fontes: Lista de carachistas de mortos - O-Ren wiki da espada