Grace is a wealthy and popular piano prodigy at the Art Academy. She holds social prominence, leading a group that assists her in bullying and ostracizing Mariel, driven by jealousy over Mariel's closeness to Oscar, whom Grace loves romantically. Flashbacks reveal a childhood promise of marriage between Grace and Oscar, with their families expecting an arranged union. As she matured, Grace's personality grew domineering and mean-spirited, causing Oscar emotional distance despite maintained superficial ties due to family pressure.

Her antagonistic role intensifies through persistent targeting of Mariel, culminating in her discovery that Mariel's "doll" is actually Memole, a living alien. This revelation occurs during a confrontation marking a pivotal shift. A severe car accident causes Grace memory loss. During recovery, Mariel helps Oscar care for her, though Grace initially doubts Mariel's sincerity. Memole views the accident as potential karmic retribution, countered by Grace's grandfather advocating compassion. The experience catalyzes Grace's transformation.

Following the accident and introspection, Grace undergoes a Heel–Face Turn. She abandons her bullying, ceases targeting Mariel, and actively works to make amends. Mariel, acknowledging Grace's enduring feelings for Oscar, encourages their reconciliation, leading to peace between Oscar and Grace. By the series' conclusion, Grace evolves from antagonist to a supportive friend for Mariel and a Secret-Keeper, joining Mariel and Oscar in safeguarding the existence of Memole and the other Riruru aliens on Earth.