Instant Teen: Just Add Nuts

Instant Teen: Just Add Nuts (おとな に ナッツ, Otona ni Nattsu, lit. "Nuts To Make You An Adult") is a shōjo manga by Haruka Fukushima. The manga was published in English by Tokyopop.

In 2009, a spinoff was serialized in Nakayoshi called おとなにナッツー (Otona ni Nattsu ni lit. Nuts To Make You An Adult Two), with different characters; it has just one volume.

Plot
Natsumi Kawashima is a young fifth grader who longs to grow up and become a woman. While crushing on an older hair stylist, Natsumi is embarrassed because of her age. Natsumi runs away and steals some nuts from a lady handing them out to women only in the mall. When Natsumi is eating the nuts, she notices that some of them are pink. The next morning, Natsumi wakes up with the body of a beautiful young woman. She does not notice her body transformation until her older crush, Toji Yashiki, asks her about being a hair model. They go on a fabulous date after Yashiki gives her a makeover. The next day, Natsumi is "kidnapped" by some college students and finds out that one of them created the nuts she ate earlier. Dr. Yunosuke Morinomiya, the creator of the nuts, forbids Natsumi from eating them due to unknown side-effects. Natsumi disobeys the orders to say goodbye to Yashiki. When Natsumi plans to tell him good bye, he takes her on a cruise for the salon he works at. But while on the cruise, the nuts' effect wears off but instead, Natsumi turns into a baby! Dr. Morinomiya and Natsumi's neighbor, Asuma Yoneyama, return her back to normal. Natsumi says goodbye to Yashiki for good without telling him about the nuts or her real age. Natsumi learns her lesson and as she and Asuma play videogames, she finds out that Asuma sent pictures of her as a young woman to a modeling contest so he could get a game. Natsumi gets a package in the mail and inside it is the nuts. Dr. Morinomiya sent them to her because he finished his project and the nuts no longer had side effects. Natsumi uses the nuts for the photo shoot in the Southern Islands that she had won from the contest.

Later on in the series Natsumi finds out that Asuma actually likes her. Many letters were sent to the author because many people wanted Asuma to turn into a man.