It all started from the Votings for Presidential of Dance Club. 

Got7 the most popular Boy Group in their University, they are in their 4th semester. The Playboys, they like to play with Girl's Hearts. They went like that because of their past. They have same pasts, that's why they really understands each others feelings. 

One day the Principal Announced that the Election for the President of Dance Club and Singing Club where now open.

A member of Got7 runs for the Position of President for the Dance Club.

Which Sulli of F(x) band also runnings for. F(x) just debuted months thats why they were not that popular, but well known as the geniuses of the university. 

Sulli is the one thats incharge of dancing in f(x), sulli loves dancing than singing. She is major in Singing in her last semester. And that's why her and her friends formed Band. 

Then the selectionhas come. Since Mark is more Popular, he wins. 

Sulli Cried the whole day because of that, she can't accept that Got7's Mark wins.

Luna, she is also a member of F(x) als loses to a member of Got7 named Youngjae. 

Luna is the Main Vocal of the F(x) while Youngjae also is a Main Vocal of Got7.

they compete for the position of president in Singing Club. And as the same situation with Sulli, the popularity is the reason thats why the members of Got7 always wins. 

The other members of F(x), knows wha they feel, because they've been admiring that positions since they were in the past semesters. 

Since thay day. They named the got7 members as their RIVALS.