The main character is a junior high student named Jun, a brilliant Child Prodigy who can create her own inventions. She falls in love with a much taller and older bad boy named Rei Kano (nicknamed Zero) who is a bit Book Dumb and only cares about motorbikes. While a relationship between them appears to be impossible, the two find a connection due to their common interest in mechanics.
The manga was only published in Japan, while the anime version was also broadcast in some European countries and is also known as Vas-y Julie! (France), Juny Peperina Inventatutto (Italy), Los Inventos de Eva (Spain), and Step Jun (Greece).
The series provides examples of:
- All Girls Want Bad Boys: Jun's crush on rebellious biker Zero. Although Zero is a Jerk with a Heart of Gold, he has a strong bad boy appeal.
- Book Dumb: Zero gets poor grades and frequently skips classes.
- Cool Old Lady: Zero's energetic grandmother, who is very fond of Jun.
- Expy: Jun looks like a redheaded Arale. Other than that, they are both bubbly and innocent child prodigies who are Good with Numbers and have a strong association with robots and inventions (Jun is an inventor who creates robots, Arale is a robot created by an inventor).
- Gadgeteer Genius: Jun spends most of her time building robots and all kinds of gadgets, often just for fun.
- Height Angst: Jun has this due to being much shorter than her classmates.
- Huge Guy, Tiny Girl: Zero is considerably bigger than Jun.
- Innocent Prodigy: Despite Jun's great intelligence, but she can be immature, childish, and even clumsy on occasion. She has some Kiddie Kid tendencies in both appearance and personality.
- Older than They Look: Jun looks like a little girl, but according to the Japanese wiki, she is 14 and known for being very short. This works better, considering her Ship Tease with a visibly older boy.
- Opposites Attract: Short Book Smart Jun and tall Book Dumb Zero. It's implied Zero likes her back.
- Robot Buddy: Yukinosuke, a male robot created by Jun herself. A female robot will be created later.
- Shorter Means Smarter: Jun is a tiny girl and a Child Prodigy who is much smarter than her Love Interest and all her taller classmates.
- Teen Genius: While she looks younger, Jun is actually 14, so she qualifies as a teenage prodigy and exceptional Gadgeteer Genius.