Legendary Panty Mask (1991)

Original title: 美少女探偵 まぼろしパンティ

An old western town is populated entirely by cute young Catholic schoolgirls and shotgun toting nuns who have killed off the entire male population, the nuns teach their female students that all men are evil. The girls are championed by a superhero named "Panty Mask" who shows up wearing a leather bikini and a pair of leather girls' underwear on her face. The nuns worship an ice carving of Christ which has the ability to make their soft drinks cold (which they don't share with the students).