Kate, a senior who is about to go abroad in her senior year of high school, and Yang Zifanfan, a low-achieving sophomore in high school in a small city. How ambiguous and entangled will the "siblings" who are 380 days apart be? After two people who met as strangers, after experiencing so much together, will they end up as strangers, or will they create a rare and beautiful sister-brother relationship? This work is my debut work, and it also served as Yang Zifanfan's 17th birthday gift. This article is based on my personal real experience and changed narrative, so there are some logical differences and errors. Please point them out and I will correct them as soon as possible. Thanks.