Lean Joker

Lean Joker is the last member of the Class Zero elite, his number is No. 0, he is seen working with Tiz, No. 10 of the same class. A huge difference between Joker from the rest of the class is that he is wearing a Milities uniform, it remains unknown why he does so, however him and Tiz seem to have a strong relationship with Arecia Al'racia even more that the other members of Class Zero themselves.

Story
At some point in the game after Machina and Rem turn into crystal, Joker and Tiz are the ones that ask Arecia to release them from such prision and to erase the Crystals from history to prevent the world to fall in ruin.

Trivia

 * Along with Machina and Rem, Lean Joker is the only member of Class Zero who's real name is revealed.
 * Since Lean is dressed in Milities uniform his real nationality remains a mystery, either beign a spy from Rubrum or actually a member of Milities working as a double agent.