Cocktail Ponytail

This is one of Hoshisato's first series, a romantic comedy about a youthful, energetic, and reluctant transforming high school girl hero named Saiko. A passing alien sees her courageously defending someone in a fight and is impressed with her sense of justice. He gives her a small handheld device which allows her to change into "Lady Tail", a futuristic superhero sporting a ponytail.