Gekkō is a second-year middle school student at Gessen Girls' Academy. She initially appears alongside her half-sister Senkō as a tertiary antagonist in the Master Story Arc. Discovering Kurokage's diary in the school library, which outlined extreme ideals of justice, she and Senkō adopted these ideals as their motivation and began operating under Fubuki's command. Physically, Gekkō possesses pale skin, silver-grey long hair, and green eyes. She wears the standard Gessen Girls' Academy Middle School uniform normally. Her transformed attire consists of a gold and black sleeveless suit with a white vest and yellow jacket, a black apron, detached yellow sleeves featuring black diamond plates, long yellow pants, and yellow boots, all adorned with multiple moon crescent symbols. Gekkō maintains a façade as a perfect, admired student, concealing her true fanatical dedication to Kurokage's ideals. Despite her brutality in pursuing her goals, an underlying positive, kind, and justice-driven personality exists. A prior sense of emptiness defined her before finding the diary. Within the anime storyline, Gekkō and Senkō ambush the Hanzō Academy team, capturing all members except Asuka. They organize the Shinobi Masters tournament, using the captured shinobi as leverage to challenge other academies. Defeated by Yumi and Asuka in the finals and subsequently abandoned by Fubuki, they apologize to the Hanzō team. When Fubuki launches a Yōma invasion, the sisters confront her directly but are defeated. Feeling abandoned and disillusioned, they attempt suicide by jumping into a river; Yumi stops them, offering a new perspective on justice. They later join Yumi in confronting Fubuki one final time, only to be knocked unconscious by Fubuki's Yōma powers. Her key relationships include a close partnership with Senkō, coordinating plans together. She initially reveres Fubuki as a mentor but becomes adversarial after Fubuki's betrayal. An ideological clash and eventual reconciliation with Yumi serve as a catalyst for her changed worldview. Outside the main storyline, Gekkō demonstrates a passion for creating clothing and costumes, often designing event-related outfits. Her name translates to "Moonlight," reflecting the lunar motifs in her transformed attire.