Instant Teen: Just Add Nuts

Instant Teen: Just Add Nuts (2001-2003) is a Japanese shōjo manga by Haruka Fukushima published by Kodansha. 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.

Tropes included:
 * Clingy Jealous Girl - Karin
 * 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.
 * 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
 * Jerk with a Heart of Gold - Asuma
 * Older Alter Ego
 * One chapter inverts this when taking too many of the nuts turns Natsumi into a baby.
 * And also inverted in the final pages of the final chapter/epilogue (they're the same thing, really), where Natsumi and Asuma, right before, 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!
 * Nosebleed - Asuma when it comes to sex.
 * The Rival - Dr. Shinobu Nanao, for both Natsumi and Dr. Morinomiya
 * Secret Keeper - Asuma and Dr. Morinomiya