Write to the person blowing out next year's candles.
Birthdays are the one day the year looks you in the eye. Everyone asks how it feels to be older; almost nobody asks what you want the next lap to hold. So tell the one person who will genuinely care: you, one year older again, reading this with next year's cake in front of them.
Some people do this every birthday and end up with a shelf of former selves, each one sealed on the day and opened on the day. It is a strange and lovely thing to accumulate.
And it works the other way. Write it on their birthday, choose Someone else, give their name and address, and a year later, on their birthday, they get a letter from you that nobody, including us, could read a day early. They are told today that it is waiting; what it says stays yours until the day.
Encrypted in your browser. Scheduled to open one year after verified sealing; pairs need verified payment and both letters written first. Keep your private key link safe. US$5 for one letter, US$9 for two.