Board Thread:Versus Debates/@comment-3523655-20200804020538/@comment-36366948-20200818041730

He can also see what they're doing with their chakra in order to copy it which is how he copied the rasengan. Nope, he learnt the Rasengan before he got the Sharingan because the Chidori is a byproduct of Kakashi failing to add his lightning chakra nature to the Rasengan, which means he knew it before he invented the Chidori which is pre-Sharingan. It's likely that Minato/Jiraiya probably taught Kakashi the Rasengan lol.