Step into the portal at the base of Konohana to reach the River of the Heavens. The game can be saved at the Origin Mirror before moving north through the area. Follow Issun's instructions to break some pots and wall jump up a ledge before what appears to be a dead-end to the north is reached as the path runs into a body of water. Look to the north-east for a hill with a torii. At the top of the hill, Issun will instruct Amaterasu to draw the missing star in the constellation. To do so, simply dot the left end of the line and she will learn Rejuvenation.