SORA.

Sora and Umi (both played by Lee Tae-kyung) who were born to a Japanese father and a Korean mother and raised in South Korea. Sora now lives in Shanghai and works as an illustrator. When she meets a Japanese guy named Mochizuki, they become close. This is when her sibling Umi visits. Umi was born inter-sex and had undergone gender reassignment surgery to become a woman. Umi encourages Sora and Mochizuki to fall in love, but Sora becomes mentally unstable.