Fight opponents for 20 levels, the HP of your team does not regenerate. At a certain stage, you will be able to spend gold to increase your HP, ATK, DEF so that your team doesn't die and you can win your fights.
At each fight victory, you will get back materials to improve your Jinchurikis.
Note: The last fight is against your own team so it is harder.
The Mizukage Shop allows you to buy purple Jinchuriki and Orange Jinchuriki fragment chests.