St. Cross Academy is divided into 2 faction:

The Blacks

They are called The Fighters.

Blacks commonly wear jackets or their Varsity jackets.

They rule the Sports and Dance Division of the Academy.

The Rulers:

King: Kim Jongin

Queen: Lee Taemin

Jack: Kim Jongdae

Knights: Kim Seokjin, Park Chanyeol,Choi Junhong, No Minwoo and Lee Chanhee

The Whites

They are called The Geniuses.

Whites commonly wear vest or their complete uniform.

They rule the Academic and Music Division of the Academy.

The Rulers:

Queen: Kim Joonmyeon

King: Wu Yifan

Jack: Kim Minseok

Knights: Do Kyungsoo, Huang Zitao,Park Jimin, Lee Jeongmin and Jo Youngmin

But there are exceptions in their school, unknown to everyone there is another faction where in only those
who are called on they first day are able to join. The special faction is called The Grey.

Greys are special and because of that they only few.

Greys don't wear uniforms and have so many priviledge in the Academy.

And Luhan is one of them.

Luhan is nothing but a walking disaster, and he hates everyone who tosses him around for his face,

so why St. Cross Academy ask him to be their student?

Maybe because he can change someone,  but who is it?