Yeah, but that doesn't explain why Tobi would've needed the First's DNA. I'm pretty sure that's what he told Konan. It's right here:Danzo only took Senju DNA to have the charkra to control such a large number of sharingan and to be able to control the Nine tails with the First Power
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So I'm sure that Danzo needed it to use Izanagi and I would think that Izanami would work the same way.