Rainbow Stone

The rainbow stone is a rare gem that is shown in Episode 24. Tsukiko Yamada (Gretchen in the English dub) wanted to show off the stone at Zakuro's fashion show to prove to people that the value of a gem isn't the price but how beautiful it can make a girl look. However, none of her superiors believed her due the stone's plain appearance and her being a bad worker, thus they never gave it a chance.

In Mew Mew Power, Gretchen says that she used Rainbow Stone to design her own line of jewelry but nobody wants to give it a chance due her only being an intern worker and the stone being described as "ugly".

In both the original and the English dub, it was suspected that the Rainbow Stone could be the true form of Mew Aqua/Blue Aqua but after a fight between the Mew Mews and the Aliens, it turns out that the stone only has the ability to react to it but it's not a Mew Aqua itself.

After the aliens leave, the fashion show continued and Tsukiko, with the help of Zakuro, got the courage to model the Rainbow Stone herself, thus proving the stone's power to bring out a girl's inner beauty to be true.