A pretty major difference between anime and western animation is the amount of detail Japanese productions put into character profiles and backstories. For just about any significant anime character, you can be sure the creators have decided on things such as a family name, exact height in centimeters, favorite food, and, in the case of sex-appeal female characters, bust, waist, and hip measurements.
If nothing else, characters almost always have an official birthday, even if there’s never an episode highlighting it or any other part of the story affected by, for instance, Attack on Titan’s Levi being born on December 25. Now, a fan-produced website has compiled a database of anime birthdays, allowing you to plug in your own to see which characters you could conceivably share a cake with.