Gelos begins as an executive at Criasu Corporation's Azababu branch, part of a future organization stealing Mirai Crystals to control destiny. She possesses short dark green hair with red highlights styled in a bob, yellow eyes with purple eyeshadow, a beauty mark under her left eye, and lipstick. Her attire typically includes a long dark red dress with black sleeves, a dark yellow coat draped like a cape, and dark red stiletto-heeled platform boots. Her villainous "dark form" features spiky hair, a dark red jacket with dark yellow spikes, a black corset, a long black skirt, a dark yellow choker, dark red knee-highs, and black heel boots. Later, as a temporary Cure, she gains a gold heart-patterned tiara, puffy hair, and white pom-pom earrings. In the restored future, she appears as a child with shorter hair and a beige triangular hairclip.

Her personality masks a delightful exterior with deep-seated insecurities. She harbors intense hatred for emotions like friendship and love and fears losing her youthful beauty. Gelos exhibits supercilious, ungrateful, and jealous tendencies, often disregarding loyal subordinates JinJin and Takumi and even firing them to advance her standing. This rejection of genuine connections fuels her descent into madness. Her core motivation is a desire to stop time to avoid aging, rooted in the belief she was only loved when young. She habitually incorporates English words or phrases into her speech, reflecting pride in this affectation.

Gelos's history includes a past friendship with JinJin and Takumi before joining Criasu. After recruiting them, she begins treating them poorly. Her early actions involve turning individuals like Aisaki Masato into Oshimaida monsters using the phrases "Hope for tomorrow, begone! Negative Wave!" to summon Prickly Powerer and "I'm ordering you! (Mou-)Oshimaida!" to transform it. She later transfers to the Azababu branch and is promoted to main manager. Manipulatively, she steals George Kurai from colleague Papple, causing Papple's despair and transformation into an Oshimaida. She also targets individuals like careless boys at a night pool, strengthening their Oshimaida forms.

Her dissatisfaction escalates upon discovering JinJin and Takumi meddling with Doctor Traum's prototype invention. She forcibly merges them into a single Oshimaida, declaring them her slaves rather than friends. This betrayal triggers her mental breakdown, leading to her dark form. On Christmas, in further instability, she swallows another Traum prototype to become a Mou-Oshimaida. JinJin and Takumi intervene, affirming their enduring friendship regardless of age. Their words cause Gelos to break down in tears, creating an opening for the Pretty Cures to purify her with the "Tomorrow With Everyone" attack. Post-purification, she accepts JinJin and Takumi back as attendants and enjoys Christmas with them.

Following redemption, Gelos assists the Cures against George Kurai, skillfully piloting a motorboat to evade Mou-Oshimaida attacks while transporting them. Later, when hope seems lost, she temporarily transforms into a Cure alongside other characters, contributing to the collective effort. In the series epilogue set 12 years later in 2030, she returns to the future as a young girl alongside Charaleet, JinJin, and Takumi, indicating reintegration into a normal life.

Culturally, Gelos ties to Japan's "Lost Decade" (1991–2000/2010), contrasting with colleague Papple's "Bubble era" style. She is modeled after the comedian Blouson Chiemi, known for portraying careerwomen from that period. Her platform boots reflect 1990s fashion trends, and the male attendants appearing during her Oshimaida summoning dances reference younger members of Blouson's comedy group.