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.

However, she had just recently cut her hair after her boyfriend berated her for fighting too much. When she transforms into Lady Tail, her ponytail comes back, which causes her to initially refuse the alien device. Eventually her sense of justice comes through and she begins using the device to transform into Lady Tail and assist those in need of protection.