Ruby is a Cocotama, a tiny god manifested from a cherished ruby ring once owned by Midori Hoshinogawa. Her formal title is "Kyu Kyu to Pika Pika Ring no Mikoto," designating her as the Ring Goddess. She appears as a lavender and ivory squirrel-like creature with a ring-shaped tail tipped by a garnet gem. Her features include pink cheeks, large sparkling blue eyes, and long curled hair partially braided and accented by a distinctive purple streak. She wears a pearl barrette decorated with a garnet rose and sports a sparkly turquoise gem on her pants.

Graceful and gentle, Ruby possesses a deep appreciation for beauty and elegance, coupled with skill in playing the piano. She maintains a generally composed demeanor but exhibits a noticeable tendency to become obsessed with aesthetically pleasing objects or concepts. Prior to joining the main Cocotama group, she resided in an antique shop, observing protagonist Haruka Hoshinogawa for about a year before Haruka became the Legendary Cocotama Contractor. Ruby ultimately revealed herself and chose to live alongside Haruka and the other Cocotamas.

She manages the Cocotama Shop within Antique Sakura, serving the Cocotama community. Ruby's magic specializes in enhancing beauty and style. She also operates under the secret identity "Ruby Karat," a phantom thief dedicated to cleaning and removing dirt. When adopting this persona, her appearance gains a violet neckerchief and an embellished barrette.