Sea Neons are small Heartless enemies resembling jellyfish that appear exclusively in Atlantica and its corresponding location in End of the World. They are essentially Atlantica's version of the Shadow Heartless; they are the weakest Heartless there, and come in numbers.
A Sea Neon may come in a group, usually with at least one Sheltering Zone nearby.
The Sea Neons are based on jellyfish, though they have a number of features that distinguish them from their real-life counterparts. While they have a number of small bluish-green tentacles dangling beneath them, they also have two massive pale blue ones in the front that allow them to deal large amounts of damage during their twist attacks. Within their light grayish-blue transparent heads and hidden behind the prominent Heartless emblem there are their sinister Heartless visages, complete with a crooked, toothy smile, bright yellow eyes, and a medium-length plume that ends in a spiral.
Kingdom Hearts Final Mix Sea Neons have warmer colors, boasting orange small tentacles, bright yellow big ones, and a reddish-black iridescent head.
The Sea Neon's name references the glowing, fluorescent appearance of some jellyfish.
Sea Neons have limited abilities, and are basically restricted to weak melee attacks by swatting with their tentacles. In their home world of Atlantica (not in the End of the World), they have no elemental resistance. A Sea Neon's most helpful ability is its relative agility in Atlantica—where Sora has a harder time moving around—combined with its ability to be spawned from a destroyed Sheltering Zone.
- Within Atlantica in Kingdom Hearts: Chain of Memories, the Sea Neon replaces the Shadow as the small Heartless battle icon.