That Whistling Youth (2017)

Yang Yi is a free-spirited girl who's homeschooled by her father, who raised her on his own after her mother passed. He homeschooled her while allowing her cousin, who is her best friend, to attend his school (He's the headmaster), out of fear of his daughter being ill-influenced, or harmed. On her birthday, Yang Yi finds her friend Ye Qing washed up on the beach, and brings her to the ER, only to find out she's in a coma. She then transfers to the all girls school as a boy to find out what brought her friend to suicide.