Other Than My Friend's Sister, Something Else

Seula has endured unrequited love for a long time, thinking she could settle for just being a friend. However, when he finds out that Areum is getting married, his world collapses. In an attempt to calm her broken heart, Seula, totally drunk, ends up calling Areum and confessing her feelings. But the next day, when she wakes up in an unknown place, completely naked... at her side is Areum's younger sister, Daun?!