The Three Beckys are three girls who used to bully Retasu Midorikawa. They pretended they were her friends so they could spend her money and get her to do their homework for them, and Lettuce is convinced that these girls will be the only friends she'll ever have because she is so shy (that is, before she meets Ichigo Momomiya, Minto Aizawa, and the other Mew Mews). The girls are seen to be spiteful and bossy.
When the three girls visited Café Mew Mew as seen in episode 3, Ichigo witnessed them picking on Retasu and faked tripping where she spilled food on them. The three girls got angry at Ichigo until Keiichiro Akasaka intervened and took the girls to get cleaned up.
In Tokyo Mew Mew, the girls were unnamed. In Mew Mew Power, they were all called Becky.