Sato

Sato (砂糖 Satō) the main mascot of Happy Happy Pretty Cure!. She needs to get the physical manifestations of hearts and happiness that she calls Amare and Gaudium in order to fuel the Train of Peace.

Backstory
Sato comes out of the sky tells Mariko, Misaki, and Kaede to get the Amare and Gaudium from other people to fuel the train of peace. At first, the Cures refuse helping her because they're using love and happiness as coal and it could be a trap to get rid of happiness, but Sato explains that Amare and Gaudium are byproducts of love and joy and not literally love and joy, so they're like "yeah, let's go".

Trivia

 * Sato used to be four characters; Heureux, Soleil, Jour, and Nuit. Particularly, Heurex, who was Mariko and Misaki's partner.