Finding Shiny Leaves
Talk to your partner Pokemon, the first Pokemon in your team and the Pokemon that follows you, while walking through tall grass alongside Routes. If your Pokemon finds a Shiny Leaf, he will perform a dance and display an exclamation mark over his head and the Shiny Leaf will be added to the Pokemon's status page.
Pokemon Nature
Your partner Pokemon's nature determines the areas where he might find Shiny Leaves. Each nature has its own set of areas where Shiny Leaves can be found, and some natures allow your partner Pokemon to find Shiny Leaves in more areas than others. Rash Pokemon, for example, can only find Shiny Leaves on Routes 11, 18, 26, 39 and 44 while Lax Pokemon can find Shiny Leaves on Routes 2, 4, 6, 28, 32, 35 and 48.
Shiny Leaf Challenge
Travel back to New Bark Town when your partner Pokemon finds a Shiny Leaf and talk to Ethan or Lyra, your counterpart characters. Ethan is available if your character is a female while Lyra is available if your character is a male. Talk to your counterpart and she will challenge you to find four more Shiny Leaves with your partner Pokemon. You must find all five Shiny Leaves with the same Pokemon to complete the challenge.
Shiny Leaf Rewards
Talk to your counterpart after finding five Shiny Leaves with a single Pokemon to receive your rewards. You will receive a star on your trainer card and your counterpart will turn the five Shiny Leaves into a Leaf Crown. The Leaf Crown is visible on your Pokemon when viewing his status screen, but has no effect other than changing his appearance.