This is a world of ABO. Sang Yu and Qing Ling have known each other since childhood and were each other's best friends. However, due to changes in Sang Yu's family, he could not keep his promise with Qing Ling and left Qing Ling. Later, when Sang Yu was in his sophomore year of high school, when his family problems calmed down, he transferred to Qing Ling's school.
Purpose: freedom to love