Board Thread:Episode Discussions/@comment-1181222-20180913151539/@comment-25122992-20180913204952

Besides other guesses, I wondered about Oro's words to Log that Mitsuki is going to develop to the "stage 2". Since the whole arc is heavily paralleling Sasuke Retrieval Mission, there's a chance Mitsuki set off to master his senjutsu abilities to a higher degree (akin to Sasuke's second stage of CS which he developed through the effords of the Sound Four) by departing to the Ryuchi Cave (which is already known to play a significant role in the arc).