Even If You Don’t Have a Third

“If We're Still Single at 30, Let's Get Married!”
A naive promise made like a joke with a childhood friend during middle school. Time passes and flows, and it's the year of turning thirty. Yoon-hwa, who was about to marry her boyfriend whom she had been dating since college, is shocked by his sudden declaration of breaking up.
While walking absentmindedly on the street, she is hit by an approaching car, and when she wakes up, she had lost 10 years of her memory, and her childhood friend is acting as her guardian. Guardian? You're my guardian?
“Are we really married?!”