Board Thread:Episode Discussions/@comment-32617252-20180429034507/@comment-33372361-20180502203652

At this point, KK being either a bastard child (since Jiraiya was fooling around with women a lot), or one of Minato's teammates are actually the thoeries that make more sense. Remember that the first one who invented Rasengan was Minato, which he based on the Tailed Beast Ball. Since it also took him three years to complete it, it would make sense if he was 'helped' or watched by one of his teammates in the process which would explain how KK knows Rasengan.