Instant Teen: Just Add Nuts (original Japanese title: Otona ni Nattsu, literally Nuts To Make You An Adult) is a Japanese shōjo manga by Haruka Fukushima, published by Kodansha in Nakayoshi from 2001 to 2002. The manga was published in English by Tokyopop; the Tokyopop edition of the manga is out of print as of August 31, 2009.
The story follows the misadventures of one Natsumi Kawashima, a fifth-grader who desires to be an adult. She eventually obtains magical nuts that allow her to transform into an attractive grown woman some time after consumption. Using this magical reagent, she manages to live out her fantasies as an adult.
The series spanned four volumes, with a serialized sequel in Nakayoshi magazine, おとなにナッツ (Nuts to Make You an Adult Two) in a single volume.
- Coming-of-Age Story: Long-term, the plot is really about Natsumi learning about what it means to be grown-up, while at the same time about her learning that she really shouldn't be rushing to grow up and to enjoy just being a kid. Oh, and also coming to terms with her feelings/love for Asuma.
- "Freaky Friday" Flip: The bonus chapter at the end of volume 2 has Natsumi and Asuma do this. Naturally, also counts as a Gender Bender Flip, given that they are opposite genders.
- Genki Girl: Natsumi.
- Nosebleed: Asuma when it comes to sex.
- Older Alter Ego:
- One chapter inverts this when taking too many of the nuts turns Natsumi into a baby.
- Inverted in the final pages of the final chapter/epilogue (they're the same thing, really), where Natsumi and Asuma, right before their wedding, are (accidentally) given, instead of "relaxation nuts", a new variant that turns them into kids; given that the epilogue takes place after they graduate, this naturally means that they turn into their fifth-grade bodies!
- The Rival: Dr. Shinobu Nanao, for both Natsumi and Dr. Morinomiya Dr. Nanao was a rival scientist of Dr. Morinomiya, who created nuts that could be used to turn herself into a beautiful woman. Because of this she competed in many beauty contests against Natsumi.