Jung Yi Hae,Fifteen y.o Girl Is A Trainee In TS Ent And Going To Debut As One Of The Main Rapper In Her Group.On One Day,She Meet A Very Caring Man That Really Pays Attention And Always Assure Her That He Is Her Oppa,Bang Yongguk.Even Tho Yongguk Is Yi Hae's Sunbae,Yongguk Always Think That Yi Hae Is Her Dongsaeng And Thats What Keep Both Of Them Together.Alot Of Things Ahead Them Thats Trying To Seperate Them,But Wil They Still Be Together As One?Looking On Each Others Back?