Luck with minor amount of dexterity and power are the highlights of being a thief. Thieves are apt to using
special skills such as sneak attacks and hiding in the battles.

Requirement: Level 10, with 25 DEX

Proceed to the Thieves' Hideaway at a basement of a cafe in Kerning City. In there, you'll find the Dark Lord. Talk to him, and you'll be
advance as Thief if you've the requirement stats.