"Margaret" received heavenly orders to protect the "Tower of the Water Deity" as its Guardian. But she's an easygoing girl. Guardians are usually strong because they're masters of a variety of magic and martial arts. Margaret, however, is poor at magic, so she uses two large-sized pistols that fire magical bullets. She is full of vitality and has built up her body, but she's learned no martial arts or stuck to anything like that. In short, she has slacked in her everyday duty as the Guardian.
Her laziness has let the Tower of the Water Deity fill with monsters and its water become polluted, troubling the humans and angering the gods. Apollo, in charge of communication between the Guardian and all gods, has ordered Margaret to reveal the source of the pollution and wipe out the monsters.
The story of Margaret begins now...