A Promise of Derivation

A few years ago, a girl helped a boy, but she doesn't remember him. He later searched for her, but couldn't find her.

Fate brings them together again in Rancity, and they fall in love.

During this time, the girl fails her college entrance exams and doesn't get into the university she had hoped for. Their promise dissolves like a bubble. While living apart, a misunderstanding forces them to break up. Later, the girl leaves Rancity, a city she had only just gotten used to, for Qingcheng, a city a thousand miles away.

Here, she can grow freely. She has never told him how much she likes him.

He has waited all these years for just one answer.

"Why did we break up?"