Haechan's twin sister

Haechan's sister arrives in Korea after 5 years of studying abroad in LA. The problem is that no one in the group knows of her existence.

How will the group take it?

Will she be accepted?

Haechan and his sister made one promise before her arrival, 'Never date anyone in their twins friend group'

Will she keep her promise?

' How can I keep a promise when that promise is to hard to keep. ' - Hoya