Coincidentally, an earthquake killed the entire Grade 1 and 4 classes.
Coincidentally, everyone in Class 1 and Class 4 traveled through time together.
After classmate Su Yan finally woke up, she found that she had become a boy [what the hell] and was also a young prince.
Su Yan: Am I now responsible for saving my poor people (classmates) from danger?
Lu Chuan: Be good.
Purpose: The importance of friendship