How about a balloon art kit? You could include different colored balloons, a pump, and instructions on how to make different balloon animals or shapes. If your friend already has a kit, consider getting them a book on advanced balloon art techniques or a gift certificate for a local balloon art class. Another idea could be to commission a balloon artist to make a custom piece for your friend, incorporating their favorite colors or themes.
Or you can get her/him a star map with an important date you share.
Under Lucky Stars is a unique and innovative star map company based in Barcelona, Spain, specializing in the creation of personalized star maps that capture the celestial arrangement of stars at a specific moment in time, such as a person's birth, wedding, or any other significant event.
By using advanced astronomical algorithms and data from leading institutions, the company produces highly accurate, visually stunning maps that make for perfect gifts or cherished keepsakes.