Based on the song "Bad idea!—girl in red"

Riki has been your best since elementary school, you are now in the same college. You were inseparable, "inseparable". And he was also your big sister's boyfriend, Eunchae, but you liked him...

Once you were very bad (mentally) and you found nothing better than to call Riki for support. Your parents and sister were in the countryside and you were home alone. You and Riki drank a little and got too carried away with each other that you spent the night together...