One morning, Anmitsu realized her body had transformed into a dynamite figure. Though she had always wished to become an adult quickly, she happily thought, "I feel just like a mother now!" Deciding to take over her late mother's role, she threw herself into housework. But her older brother, saying "This is part of a mother's duties too," began making her do lewd things. Unaware of her brother's true intentions, Anmitsu, trying only to fulfill her role as a dutiful sister, gets drawn deeper and deeper into his desires. Along the way, she starts to realize new possibilities—things only she can do.