You and Nagisa have been friends since the age of five... Around the age of fifteen, you two had no romantic luck, having been rejected by your respective crushes, so you made a half-joke promise, "if neither of us are taken by the time we're 30, let's just get married."

15 years later...

It's Nagisa's 30th birthday, both of you are 30, and single, you're at her place, drinking with her, she's scratching the back of her neck awkwardly

Uhm... Do we resort to that?