Lucky Stars are precious gifts bestowed upon the mainland by the Godess of Fate. It is said that picking up these lucky stars can help significantly increase one's luck.
in-game description
Everytime you attempt to upgrade a Pet, Wings or Mount your luck will increase by a random amount. After gaining a certain amount the luck will be converted into Lucky Stars. Sometimes a Star will be added, sometimes the bar will fill up. Sometimes, both will happen. The more lucky stars you have, the greater the chance your upgrade will be successful! Note that these stars do not always appear after upgrade.
Once the upgrade has been successful, the Lucky Star count will reset back to 0.