You He Bu Ke

Ah-cheng and Cheng-hsin are good friends with opposite personalities. Nini is Ah-cheng's beloved sister, and Cheng-hsin treated her like his own sister, too. Their happy life together lasted until Cheng-hsin suddenly transferred away during high school and they lost touch with each other.

Ten years later, Nini enters university, only to meet Cheng-hsin again by chance. That was when she found out the kind Cheng-hsin has been hiding a painful secret, and Nini became determined to help Cheng-hsin's dream come true.

(Source: WEBTOON, translated)