Lucy Grill, younger sister of Peter Grill, once shared a close bond with him during their childhood, though their relationship frayed as her notoriety for ruthlessly punishing infidelity grew. Witnessing their father’s repeated betrayals of their mother ignited her vehement hatred for cheaters, shaping her merciless approach to disloyalty. Peter now fears her wrath should she uncover his secret liaisons, aware her retribution could be lethal.

Her striking features include short blonde hair, piercing blue eyes, and an imposing dark blue armor set from the "Major Armor of the Zodiac" series, paired with a weathered black cape and spiked headbands. Twin swords, "Genocide Bringer," rest on her back, tools emblematic of her combat-driven existence.

Adoptive sister Gobuko Nggiell, a goblin raised alongside Lucy and Peter, was torn from their family by knights during their youth. Lucy mourned her as dead until their tearful reunion years later, a testament to her fierce loyalty to those she considers kin—a stark contrast to her unforgiving persona toward betrayers.

Her traumatic past culminated in brutally confronting their philandering father, an act that crystallized her zero-tolerance philosophy. This history fuels her vigilance over Peter’s relationship with Luvelia Sanctos; discovering proof of his infidelity once drove her to assault him, showcasing her refusal to spare even family from judgment.

Within the series, she looms as both a moral counterweight and a destabilizing force in Peter’s chaotic romantic entanglements. Her actions amplify the repercussions of his choices, weaving threads of fractured trust and the enduring scars of betrayal into the narrative’s exploration of family and trauma.