The initial plan was to get an item that give you an important boost to any stat/skill as a gift...but this is an opportunity to design a special quest that is triggered that day instead. I'll start thinking about that
I'll be honest: I totally forgot about this, it's a thing I planned when I designed the character creation screen but left out while I was doing the rest of the game. But now that you mention it, it's an opportuinity to have a special mission/quest, or why not, date with the current love interest.
Fun fact: The default birthday is the actual day that I started this project on 2020. The main screen of this game (it was just a black screen with some letters back them. The game didn't had a name yet) was my hello world project on twine. A lot has happened since then.