Peach Girl is a high school drama centered on Momo Adachi. A former member of the swim team, Momo tans easily and her hair is bleached out; unfortunately, she is stereotyped by her ignorant classmates, and is forced to endure rumors about being a playgirl. Her only friend is Sae, who is actually responsible for spreading the nasty gossip due to her jealousy of Momo. Momo is in love with Toji, a taciturn baseball player, but the scheming Sae also has her sights set on the boy. Momo's life is further complicated with the introduction of Kairi Okayasu, a wise-cracking playboy who is determined to make her his. He reveals to Momo that she had saved him from drowning the summer before high school started.
Things become even more complicated when Sae, in an attempt to make Momo miserable, spreads rumors about Momo and Kairi making out. The rumor about the kiss between the two is true, but it was Kairi who initiated it while Momo remained stunned by the interaction. When Toji is hospitalized, Sae convinces Toji to break up with Momo. They soon get back together, but Sae later tries to make their relationship complicated again by threatening to discredit Momo with her newly acquired access to the mass media. Though Toji is defiant to begin with, he reluctantly breaks up with Momo in order to protect her. Momo is heartbroken at first, particularly due to not knowing it is part of Sae's schemes. However, she eventually begins dating Kairi, whom she had previously considered annoying, and soon begins to fall in love with him.
When it is revealed to Momo why Toji broke up with her, Momo is left to choose between Toji and Kairi. More problems arise and the love triangle intensifies.