Bubu, Eodikkaji Ganeunghae?

The Song family's true biological daughter appears, shaking Juha's world. Seeking an escape from an unwelcoming home, Juha embarks on a series of blind dates until she meets Sahyeon, who boldly suggests setting a wedding date within minutes of their first date. Just as Juha starts to develop feelings for him, her cunning younger sister—who has already taken everything else from her—declares her intention to marry him instead.

(Source: webtoons)