Any of your characters that shares the same birthday as yours?
Oddly enough, no, if you don't count my "persona" which is basically just me.
How do you decide your characters' birthdays?* Is it a requirement for your characters to have a birthdate, or not?
I have three methods: Name days; "holidays" that relate to the character or I choose them by whichever zodiac fits the character best.
How often do you celebrate your characters' birthdays and do you usually prepare anything for them?
Haha, barely ever. Only a few certain ones. And usually I do nothing. I might draw doodles sometimes. Or work on their profiles. As a present.
And are you good at remembering their birthdays?
Eeeeehh... That's why I have a calendar.