Shine Sprites are objects that function similarly to Power Stars in the way that they are collected. They act as guardians of Isle Delfino and are the key "collecting" object in Super Mario Sunshine. Shine Sprites gather at the Shine Gate found at the center of the island and help create the sunlight there.
In the plot of Super Mario Sunshine Edit
Prior to the game's events, Bowser Jr. attacks the Shine Gate with graffiti, causing the Shine Sprites to scatter across the island. When Mario arrives, the locals think that the plumber has created the graffiti and they make him spend time in prison. They make him collect all the Shine Sprites on the island as community service. 120 of them can be found all over the island, with some requiring a certain task to reveal them like defeating a boss or revealing a pathway.