The currency for the Magical World in Sugar Sugar Rune as well as their power supply. The candidates for the Magical World's Queen has to collect the most of these to win the throne.
In both worlds (Magical and Human), Crystal Hearts come from both humans and witches and can be released with a witch's powers. Their color depends on which mood the human/witch is in.
Crystal hearts can be used for currency called "Ecure" in order to purchase anything from the magical world. They can also be used as an power source as mentioned by Queen Candy in a volume of the Sugar Sugar Rune manga.
In the Magical World, a couple can be officially married by swapping each other's crystal hearts. However, this cannot be reversed, and in attempted, it could end up killing them.
Three types of special hearts also exist in both the SSR franchise. Noir (Black) Hearts, Rainbow Hearts, and Blanc (White) Hearts. Noir hearts exist when a human/witch is jealous or has a hatred for someone. They cannot be collected as Ecure and can also hurt witches much more than ogres, whom are the rouge witches of the magical world. They can be turned into white hearts by a "Filter", which a rare amount of witches are. When a white heart is given to a familiar, the familiar can change back to their human form. For example, in the conclusion of volume 6 of the SSR manga, when Chocolat gave Duke a white heart, Duke changed to his human form and from then on goes by the name of Poivre. Rainbow Hearts exist when someone is highly amused or when they're having fun. They are worth 500 ecure. (This only happens in the SSR anime.)
Humans can reproduce crystal hearts in a snap after they are taken by a witch. They can also swap hearts when their love is true. If a witch's heart gets taken they can be killed by this because they can only contain one crystal heart. Witches can swap hearts, but only when they confirm their marriages in the magical world. This cannot be undone and the witch has to be with his/her spouse for the rest of his/her life (it's also a reason why most witches in the magical world don't get married).
They are in order of ecure amounts.
Yellow [AKA Pee]- 5 Ecure (When in fear or surprise.)
Orange- 300 Ecure (The person has a crush on someone.)
Green- 350 Ecure (They are friends with someone.)
Pink- 1,000 Ecure (In deep desire for one's love.)
Purple- 2,500 Ecure (In an relationship of unrequited love. This can also mean that they are lustful toward someone.)
Blue- 3,000 Ecure (Respect for someone.)
Red- 5,000 Ecure (They're in passionate love with someone.)