The core of a Staryu acts as a heart for the Pokémon. It glows brightly when it is healthy and happy. When it is excited, scared or angered it will flash, increasing as the emotion intensifies. If a Staryu becomes weak, its core will grow faint and will also flash slowly when it is very sick or near death. Staryu become most active at night. When the sun goes down the core will glow its brightest. Many will float from the seafloor to the surface and align themselves with stars of the night sky as their core flickers, displaying a connection with the celestial bodies of space.