The Sword of Tosuka and Yata Mirror were artifacts that even Orochimaru was searching for and they dont come from life force. While Itachi did have a strong will, he also had a weak life force which is one of the signature traits of the Senju/Uzumaki Clan. There is nothing implying he is descendant of the Senju. Him and Sasuke share the same genetic lineage.
The strong "will" that Itachi possesses is the Will of Fire as opposed to the Curse of Hatred that the Uchiha are claimed to have by
the racist Tobirama.
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