Your & My Secret, Volume 1 — Ai Morinaga

High schooler Nanako Momoi may be petite and adorable, but she is far from sweet -- she is obnoxious, violent and has the table manners of a wild boar. Akira Uehara, a dainty, feminine boy has, for some mysterious reason, developed quite a crush on her. One day, Akira stumbles upon Nanako's grandfather, a man best described as a mad scientist. He is performing an experiment on Nanako, but Akira manages to get in the way...and suddenly finds that he and Nanako have switched bodies! Akira, the now dainty and feminine female, is desperate to get back into his old body, especially after one of his long-time friends starts flirting with him. Switching back may prove difficult, though. It looks like Nanako is starting to enjoy life as a guy!