Mero and her twin sister Milo serve Cardinal Lodra, alchemizing Crimson Pact Goblins for his plan to raid Azpire. Their creations directly cause the goblin attacks threatening the city. During the assault, the twins accidentally drop and shatter the control crystal, causing the goblins to turn on them. Taichi intervenes and saves them from this peril. Rescued, Mero and Milo defect from Lodra and join the adventurers' guild, aligning with Taichi's group.

Both twins specialize in Earth Magic, primarily using the "Falldown" spell to create potholes and trap enemies, sharing identical elemental earth abilities. Early on, they display unsettling traits, expressing excitement at the prospect of goblins killing and raping civilians. Their defection shifts their allegiance but does not negate their initial antagonistic role. Design-wise, they share similar appearances as twins, featuring ponytails and hair antennae, reinforcing their matched-pair role.