To Her (2017)

Gwang-ho is bored except for the time he’s taking off his girlfriend’s underwear. He visits his Seoul home at the news that his grandfather is dying. Amidst the awkwardness, he remembers something. Ji-yoon is his cousin who has grown up to be a young lady. Gwang-ho is attracted to the fully grown woman and the same is said for Ji-yoon. Cousin Sister 사촌여동생