Loco is the strongest Rook and one of the first Chess Pieces introduced. Her name signifies a patron of healers in the Voodoo religion, referencing her ÄRM Straw Doll (Spikes and Hammer). Born 32 years before the main events of the series, Loco was a Pawn at age 26, the lowest rank in the Chess Pieces. During an attack on an unnamed town, her only Weapon ÄRM, the Ring Dagger, was broken, leaving her defenseless.
While wandering through the chaotic village, she encountered a cloaked figure, resembling a midget, carrying a large suitcase. The mysterious person asked if she wanted strength, to which Loco replied that she only desired power to fight with. The figure then handed her the suitcase, revealing it contained seven Darkness ÄRMs. However, using these ÄRMs came at a cost: reversed aging. Shortly after giving Loco the suitcase, the cloaked figure perished due to the ÄRMs' effects.
With the newfound power from the Darkness ÄRMs, Loco rose through the ranks to become the strongest Rook. Nevertheless, the use of these ÄRMs had severe consequences, as her body was transformed into that of a young child by the start of the series.
