Stories are special tasks that you have to complete in order to receive various unique Rewards and progress an Event's storyline.
You can find your Stories and Side Stories by tapping on the cell phone icon in the lower left hand corner of the PIMD main screen. If the phone is ringing, you have a new Story to start!
Please note, you won't begin seeing Event stories until you’ve completed the tutorial story “Participate in a Party with your Club".
In the Stories menu you will be able to see all of your available stories. Stories can be currently in progress, awaiting activation, or be completed and awaiting for you to collect your Rewards. In the History tab you can review all of the Stories you've completed so far.
Please note that Side Stories are released gradually as an event goes on, and each one will often have a few tiers.