Sister's Diary (2020)

Ga-eun and Su-ho grew up like brothers and sisters. However, Su-ho never showed that he likes Ga-eun ever since they were young. One day, Suho accidentally found Ga-eun's diary and found out that she also likes him. Su-ho reveals his feelings to Ga-eun. Ga-eun is not his real sibling, but to protect their parents, she rejects him...