Ok this is just a thought so.....here i go.
when Kakashi showed Naruto that he knew Resangan
One Manga Naruto Chapter 321 Page 08
He said he developed Raikiri because he couldn't combine his lightning chakra with Resangan
One Manga Naruto Chapter 321 Page 09
He also said in the middle row on the left Kakashi says " Just regular 'spacial recomposition' has a 'rank A' acquisition level... At just that level i can somehow copy it..."
One Manga Naruto Chapter 321 Page 10
which made me think about Raikiri, he said that he developed Raikiri because he couldn't combine his 'Elemental Recomposed Lightning Chakra' with the 'Spatially Recomposed' chakra of the Rasengan. And he also said that he could somehow copy it at that level so what about in the Gaiden series!
One Manga Naruto Chapter 239 Page 17
One Manga Naruto Chapter 239 Pages 18-19
In the first link it shows Kakashi saying that it was time to try out his new technique and in the second one it actually shows him conjure it into his hand.
What i was thinking was how could Kakashi develop Raikiri if he hadn't already 'copied' Minato's Rasengan for he did not have the Sharingan to use to copy the Rasengan.
what do ya think?
If this doesn't make sense than im soory its the first time ive done something like this.