The North City of Time, Where the South Wind Blows

The story is set in a largely fictional world. The author is lazy and doesn't want to look up any relevant information. Sorry. (This story idea came to me a few years ago, so some parts are pretty awkward.)

The main plot follows Sui Nanfeng, who accidentally discovers that her older brother, Gu Beicheng, isn't her biological brother. After starting university, she begins investigating the truth.