Mariah Grene fulfills the role of bodyguard for Kokomi Kikyōin. She is the younger sister of Maeve Hoshisato, creating a direct familial tie that establishes her as the sister-in-law of Mamoru Hoshisato and the aunt of Kana Hoshisato and Yumemi Hoshisato.

Her appearance features precisely cut neck-length platinum blond hair, styled to fall predominantly on her right side, striking red eyes, and a distinct beauty mark beneath her left eye. She consistently wears red lipstick. Her signature attire is a scarlet red button-up short skirt outfit, consistently accessorized with a black choker and red high-heeled shoes.

Mariah generally maintains a calm demeanor. However, her protective instincts override her usual composure when Kokomi Kikyōin faces danger, shifting her focus entirely to her defensive duties.