Mahou Shoujo? Naria Girls

The girls meet a new magical girl, Usagi! But when the new girl turns out to be a monster, they'll have to become "a magical girl who's anxious to fight the enemy that's right in front of them, and a magical girl who's started to get worried about things at the worst possible time, and a perverted magical girl who's getting excited to realize that he's actually a boy!" Can they break out of the spell and transform by giving a plausible explanation for what they'd do with 150 crabs? (Source: Crunchyroll)