My Sister the Werebeast

Something strange is happening to Peanut.
But Mira and Rosie can handle it! These two perfectly ordinary, capable sisters are fully confident they can study for their school's upcoming combat trials and care for their adorable baby sister, Peanut. So, what if she cries so hard she floods the entire house? Or randomly breathes fire? Or transforms into a (very soft) menacing creature? Mira and Rosie will just hide Peanut's powers until their parents come back, and they'll know what to do. Right?
To make matters worse, rumors of a werebeast attract the attention of a monster hunter. And there's something unusual about their seemingly quiet town.