Instructions
Visit Katie's Clothing Shop in the East Village of Autumn Bay. Katie, or Kyouko, is a Japanese tailor who sells a variety of unique clothing items. If you befriend Katie, she allows you to design clothes in her shop.
Speak to her to accept the "The Vanished Body" quest. Katie tells you that there was a mysterious person hiding out in the shop. Find out who the person was and why, and return to her. Her friendship points increase when you complete the quest.
Purchase items from the shop and speak to her frequently. Both actions raise her disposition toward you. Once she is your friend, a new "design" icon appears in her shopping basket.
Click the "Shopping Basket" and then the "Design" icon.
Design your own shirt pattern using the on-screen tools and the stylus. Save the changes. Designs are saved and put on display in Katie's shop.