Done so funnily in the first episode of the anime series. It's a tradition to Magical Girls to have a dedicated Transformation Sequence; Nina is no exception. After Nina does her transformation she gives her standard wink to the camera followed by Ayu snapping her back to business.
Can't Hold His Liquor: Nina discovers her magic potential while under the influence during the bar scene. Ayu and Yuta are not amused, as they see it as careless violation of the masquerade they're supposed to maintain (Ayu as Secret Keeper, and Nina and Yuta as magic users). Indeed, Nina was lucky to not be fined, let alone recalled, after that incident.
Crossdresser: One of Nina's magic school classmates (who turns out to be a boy) impersonates her to her friends in the epilogue, and his game is only up when Nina herself shows up as he shows off to them blatantly.
Crouching Moron, Hidden Badass: Nina, in the manga. During a battle with Sayaka in the school gym, Nina trips and leaves herself open to attack. Sayaka takes the opportunity to throw magic and ends up hitting Leo. Nina gets pissed and accidentally blows a ginormous hole in the ceiling.
Gender Bender: The first spell Nina casts on Ayu after Ayu asks for a spell that will make her stronger so she can beat the boy's tennis club is to turn Ayu into a boy. All this achieves is Ayu's timing and balance being thrown off due the height and upper body strength increase. Later on Nina and Ayu become boys temporarily for mildly convoluted reasons surrounding a triple date.
Parental Obliviousness: Yuta's adult sister Mita gives Ayu and Nina magic vitamin pills which turns them into scantily clad, busty adults so they can go to a bar! What do Nina's foster parents say about this? "Have a good time!" It should be noted, though, that Mito gave the trip as a "learning experience" for both girls.
School Idol: Ayu and Tetsushi, both respected by the entire school for their performance, diligence... and looks.
Secret Keeper: Ayu and Hiroki. Later, Tetsushi, too, when he finds out Nina's little secret with Nina's permission... only Nina herself wasn't around to witness Ayu revealing it to him, but rather a male double who immediately takes the opportunity to flagrantly violate the masquerade before Nina shows up to rebuke him for being a Jerkass to her friends because of how he's alienating them.
Shout Out: The music that plays in the anime when Nina's young triplet cousins are around sounds a lot like the theme song to The Powerpuff Girls. In fact, Wataru Yoshizumi lovesThe Powerpuff Girls.
Third-Person Person: Nina. It's inconsistent, but justified by the author in that she wanted Nina to sound a little weird; Nina justifies it by saying that the spell she used to learn Japanese wasn't perfect.
Totally Radical: The Viz "translation" has the characters saying things like "Holy sushi!" and "Galloping geishas!" in surprise. Just... no. It's worth noting that according to Anime News Network, Ultra Maniac is the only manga the person in charge of adaptation (John Lustig, who is more well known for working on Disney Comics) worked on.
Traitor Shot: Sayaka gets these after conversing with other characters, but especially after talking with Nina and Ayu.