How about a personalized crossword puzzle book? There are many places online that allow you to create a custom crossword puzzle with clues based on your friend's interests or favorite things. You could also supplement the gift with a nice pen or pencil set, a cozy blanket to snuggle up with while solving puzzles, or perhaps a subscription to a puzzle magazine like The New York Times Crossword.
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.