That overly huge zanpaktou that Ichigo had after Rukia gave him Shinigami power
was Ichigo's true zanpaktou. It was just unreleased. In fact, that sword is the
same sword that Ichigo gets after he retrieves his Shinigami powers a second time with Urahara.
This is the original sword Ichigo has in the beginning of the series:
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It's also the same sword that Byakuya cuts in half during their first encounter:
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That broken blade is the same blade Ichigo recovers at Urahara's place after he helps him gain his Shinigami powers again. Note that it's still broken from his encounter with Byakuya:
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Urahara busts it further:
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Finally, this is when Ichigo releases Zangetsu for the first time. The full-time released Zangetsu that we've all come to know came from that broken hilt - the same zanpaktou from the beginning of the series:
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(Ignore the horrendous translation error)
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