Passage of Time, Pass Through, Manage
Tying a thread to a tombstone each year will help you manage the passage of time. That way you’ll know how many years you pass through, since you’ll have one thread for each year to count.
Picture yourself coming back to the same tombstone each passing year and tying a new thread to it. You're trying to manage these feelings by keeping track of how much time passes.
けい
た, へ
None
Dealing with the passage of time can be tough, so after you tie the thread to the tombstone, each year you eat a piece of cake (けい). You already eat cake to mark the passage of time on your birthday, so why not here as well?
Maybe this is your future tombstone, and eating cake each year is a preemptive celebration of your death day! Ooh, what a spooky theory.