FUG

F.U.G (퍼그/FUG, Peogeu) is the most dangerous and secretive criminal group in The Tower. Members explicitly (though not all the time) wear the "Mark of the Slayer". The No. 1 Slayer and leader is Grace Mirchea Luslec.

FUG is often compared to the Walhaiksong (Wing Tree) because of their opposition to the 10 Families. However, whereas the Wing Tree is more of a "social club" centered around several members, FUG is a "religious organisation" centered around a single faith. Although the relationship between the two is not that good, there are a few members who are associated with both groups.

Although FUG’s true motives and goals are not clearly known, it is true without a doubt that they exist in the shadows of the Tower, hiding and corrupting.

The 10 Families forbid anyone within their Families to enter FUG, and they consider it an important duty to eliminate their members, who are known to hide within the shadows of the Middle Area.

But their dangerous status does not mean that they hold influence to contest the 10 Families. As long as the 10 Family Heads hold the contracts with the Tower’s Guardians, FUG’s influence cannot overcome the Family Heads’.

Slayers
Within their infrastructure, FUG has 11 Slayers (슬레이어, Seulaeiyeo). The origin of the name is very simple: "One who kills" Zahard and the 10 Families.

There are presently 7 Slayers active: 5 have unknown whereabouts; 2 are acclaimed as "devils", and the remaining 4 positions are vacant. All are supposedly very powerful.

"In FUG, there are those who have a grudge against 10 Families and Zahard, those who envy what they possess, and those who want to change the tower. A Slayer is a GOD who fulfills their wishes." (Ch 116)

Slayers are treated as walking Gods by FUG members.(from SIU blog)

Organization Information
FUG is an organization and not an organization at the same time. They are a group, so they can be called an organization. They have no physical forms or headquarters(unlike an organization), but membership is bound very strongly. Similar to religious faith, membership of FUG is embedded deep within its members hearts and wherever they walk or stay becomes a headquarter of FUG.

Structure
FUG itself has no structure. They are simply FUG, and they act upon faith of their Slayers. The countless groups that operate under FUG simply work toward their given goals and do not associate directly with FUG. They do not know the true form of FUG. They only accept the fact that FUG is an existence darker then their own. All Slayers, however, are united under the ultimate goal of Zahard's death. FUG members can seemingly make an "espionage" happen in order to attain seats of authority regarding Regulars on different Floors, as more than one FUG member is a Test Director

Members

 * Grace Mirchea Luslec: Founder and No. 1 Slayer of FUG.
 * Karaka: a Slayer.
 * Augusgus: Test Director of the 20th Floor, affiliated with FUG.
 * Yu Han Sung: Test Director of the 2nd Floor, affiliated with FUG.
 * Hwa Ryun: A Guide, member of FUG.
 * Ha Jinsung: High Ranker, Viole's martial arts teacher. Also taught Karaka.
 * Twenty-Fifth Baam (Alias: Jyu Viole Grace): Currently a Slayer candidate.
 * Apple: affiliated with FUG, Rachel.
 * Rachel: affiliated with FUG.
 * Beniamino Cassano: affiliated with FUG.
 * Xia Xia: affiliated with FUG.
 * Michael: affilated with FUG.

Characters who may be associated with groups operating under the FUG
Note: Some characters may be listed here if it's unclear whether they're FUG Slayers.
 * Repellista Zahard: A princess, who apparently knows of FUG's plans. However, her connection to the organization cannot be confirmed.

F.U.G