Pseudo-siblings + teacher-student + sweet story + single male and double female protagonists

Xu Nianchu, fostered in the Zhang family as a "sister", appears to be well-behaved on the surface, but secretly develops feelings for her "brother" Zhang Yu'an.

The lively and elegant Li Yuqing originally wanted to teach her "class representative Zhang" a lesson, but she developed special feelings for him during their repeated interactions. His cleverness in fighting wits and courage and his occasional tenderness gradually wavered her.

My sister's dependence is becoming more and more ambiguous, and my teacher's concern is becoming more and more subtle...

In a complicated relationship, who will be the first to lose control?