That Whistling Youth.

Yang Yi, a free-spirited girl raised and homeschooled by her overprotective father, is shocked to find her best friend and cousin, Ye Qing, unconscious on the beach from an apparent suicide attempt. To uncover the truth, Yang Yi disguises herself as a boy and secretly enrolls in Ye Qing’s all-girls school, where she uncovers the hidden pressures and secrets that may have led to her friend's coma.