Oga is a supporting character in the anime Plus-Sized Elf. She is an ogre, or oni, from another world who came to Earth for the sake of its alcohol. Her fondness for the drinks of the human world eventually gave her a beer belly, and she now works to slim down by regularly visiting the sauna at a local public bathhouse, where she often spends long stretches of time. Standing about 216 centimeters tall, she has a towering and robust build, and her superhuman strength is one of her greatest points of pride.

Her personality combines fierceness with a strong maternal side. She is extremely fond of children, and her interactions with them reveal a gentle, caring nature that contrasts with her intimidating appearance and great physical power. Her defining trait is her love of alcohol, and she is quick to insist that her weight gain is not her fault because the drinks available on Earth are simply too good to resist. She is also a devoted sauna enthusiast with a notable tolerance for heat. When Elfuda and Kuroeda first hear rumors of a female oni at the sauna and go to investigate, they are met with a wave of boiling steam from Oga, who has been sitting inside for a long time.

Within the story, Oga functions as one of the recurring otherworldly characters living on Earth. She is introduced through her encounter with Elfuda and Kuroeda at the bathhouse, and her appearances continue to center on her routine of enjoying alcohol and countering its effects through the sauna. Her role remains steady rather than undergoing major change: she stays a warm, formidable presence who indulges in Earth's pleasures while making an effort to stay in shape. Her key relationships are shown through her interactions with the other female characters, especially Elfuda and Kuroeda, along with her affection for children. Some English-language materials refer to her by the alternative name Olga.