Mami Hoshiyama is a supporting character in the Galaxy Fraulein Yuna series, introduced in the second video game Ginga Ojousama Densetsu Yuna 2: Eien no Princess and later appearing in the OVA Galaxy Fraulein Yuna Returns. She is a sixteen-year-old high school student who serves as the captain of her school's softball club. She is deeply passionate about baseball and is a devoted fan of the Yomiuri Giants, earning her the nickname Mami of the Fighting Spirit. Physically, she has short blue hair and blue eyes, stands 163 centimeters tall, weighs 49 kilograms, and her birthday is May 5.

In the story, Mami initially appears as a member of the Erika 7, a group that opposes the protagonist Yuna Kagurazaka. She attacks Yuna early on but is eventually defeated and later joins Yuna's team. After allying with Yuna, she provides guidance on how to rescue the three Wise Machines and helps in the fight against the Machine Empress. Her combat style emphasizes athleticism and physical strength, and she is often seen using a green visor device. She has a notable partnership with Miki Shiratori, another former opponent, and together they face challenges such as a hospital confrontation with Ayako. Her personality is defined by a strong competitive drive and enthusiasm for sports, though she also shows a more reserved and focused side. Her development moves from being an antagonist to a loyal ally, and she remains a capable fighter throughout the series.