While Ichigo Momomiya is on her first date with Masaya Aoyama, she is bathed in a strange light and sees herself being merged with a cat. Afterwards, she begins to display cat-like behaviors. The next day, Ichigo follows Masaya into a park, where a strange jellyfish-like creature takes over a rat's body, turning it into a monster. Ryou Shirogane saves Ichigo and gives her a pendant allowing her to transform into Mew Ichigo. With her new powers, she defeats the monster, turning it back into a normal rat. Afterwards, Ryou refuses to explain what just occurred, so the newly arrived Keiichiro Akasaka offers to do so instead.

Ryou and Keiichiro tell Ichigo that the creature she saw was a parasitic alien, called a chimera anima. To stop them, the Mew Project infused five girls with the DNA from specific endangered species, enabling the girls to become "mew mews". Ichigo begins working at Cafe Mew Mew while searching for the other four girls who bear the Mew marks. Keiichiro gives her a robot, Masha, to help with her work. While going home, Ichigo meets Mint Aizawa and her dog. Later, Ichigo visits Mint's home to return a handkerchief, but Mint's dog becomes infected by a chimera anima. During the battle, Ichigo discovers that Mint is the second mew mew, Mew Mint. They defeat the monster, returning the dog to normal. Mint joins Ichigo in working at the café.

Ichigo meets a shy and timid girl named Lettuce Midorikawa. Later at the café, Ichigo sees her with three other girls, who are trying to coerce an unwilling Lettuce to try to photograph a rumored school ghost. Ichigo "accidentally" dumps parfaits on them to get them to leave Lettuce alone. After work, Mint and Ichigo go to the school to investigate the "ghost". Instead, they find Lettuce who was afraid of being isolated because of her new powers and started "haunting" the pool. After a brief fight, Ichigo and Mint calm her by explaining her Mew powers and welcome her to the team. While Ichigo is walking home, an alien named Kish appears, steals her first kiss, and introduces himself before disappearing again.

Upset about her first kiss stolen, Ichigo avoids Aoyama, even declining a date with him. While looking for chimera animas, Masha leads her to the park where she runs into Masaya. Resolved to forget the kiss, Ichigo agrees to spend time with him. Kish attacks the park, turning a lion into a chimera anima. Ichigo leaves a worried Masaya behind as she hides to transform and fight. After Mew Mint and Mew Lettuce arrive, the three defeat the monster. When Ichigo finds Masaya, he scolds her for running away. As they walk home, he explains his worry about her, and Ichigo promises not to do it again.

The school rhythmic gymnastics team sees Ichigo avoid the path of an on-coming bus by leaping over it, and the team recruits her. A promise from Masaya to come and cheer for her at the competition changes Ichigo's participation from reluctant to enthusiastic. After Ichigo's spectacular individual performance, Kish attacks with a chimera anima. After the Mew Mews defeat the monster, competition continues; but Ichigo's performance drops during her team's round due to exhaustion from the fight. The team is happy with their second place win and names Ichigo the team's Most Valuable Player.