Sensing that the end of Koo's life was near, a grim reaper whispered his proposition to her. "I offer you strength, but you must grant me your soul in return." Koo often lamented over her fragile body, so such a proposal was far too tempting. She signed the contract and gained sublime magical powers as the reaper continued to shave off seconds from her life. Koo was not afraid, for ever since she was young, death had always been close at hand.
- Acquired as a final reward from the Arise Raid Event, started on December 26, 2013:
- Final Rank 1-50 (x2), 51-200.
- Guild Final Rank 1.
- Rereleased on March 13, 2014 in the Alchemy Card Pack.
- Rereleased on 18 April, 2014 in the Alchemy 2 Card Pack.
- Rereleased on June 19, 2014 in the Alchemy 3 Card Pack.
Gu (also spelled "Ku" and "Koo") is a family name of the Chinese and Korean people. The most common family name Gù 顾 literally means "to care for". The family name Gŭ (谷, meaning "valley"), came about when a noble family of the Zhou Dynasty was rewarded a fief in a valley area. The descendants of the family adopted the name to link their lineage to that history.