Midori is one of three daughters of Dr. Mishina, a scientist who co-founded the covert organization MET alongside Dr. Kishida. After her parents' deaths, Midori and her sisters Aoi and Kurenai inherit "Musumet" helmets engineered by their fathers to harness the power of three rainbow-colored shooting stars that struck Earth, each containing immense energy. By wearing the green helmet, Midori transforms into Musume Green (Musumet Verde).

The Musumet helmet amplifies physical strength and grants superpowers without altering the wearer's clothing beyond adding the helmet, gloves, and boots. This results in Midori and her sisters frequently engaging in battles while dressed in everyday attire—ranging from school uniforms to swimsuits—based on when duty calls. The helmets infinitely enhance the wearer's innate physical abilities, empowering them to confront threats from four rogue shooting stars endangering Earth. Operating under MET's guidance, the sisters advance their father's mission to safeguard global peace.

Midori balances her role as Musume Green with typical adolescent challenges: academic pressures, social dynamics, and romantic pursuits. Her dual life includes navigating rivalries with the affluent Saotome sisters—Marcia, Kou, and Shion.