Ten Days of Embarrassing Changes

In a world under attack from invaders from another dimension, humanity's best defenses are the Divine Beasts, powerful spirits that bind to young women and alter their bodies to give them powerful new abilities. When one girl becomes bonded to an entity known as the Fairy Mother, she is excited by the prospect of becoming a real-life superhero. Unfortunately, the transition into being something other than a human is much more confusing and strange than she is prepared to deal with. With powers centered around producing magical offspring that fight to protect her, she is hurled into a seemingly endless series of embarrassing changes that leave her questioning her humanity. On top of all of that, she is forced to deal with an overly clingy sister, a wannabe superhero that looks like a stuffed animal, and a mysterious girl with dangerous powers who threatens to draw her into a world-spanning conspiracy.
This is a 50,000+ word fantasy adventure set in the near future, filled with comedy, confusion, and heroic battles against otherworldly monsters.