The Invisibles, at first glance, appear to be quick-moving shadows, but a closer inspection reveals more than a strong resemblance to Darkside, including black skin, a similar muscular frame, and a heart-shaped hole in their torsos. However, Invisibles are much smaller than Darkside, as well as more embellished. They have sharp purple and blue horns that form the outline of a curled heart similar to the ones found in the Kingdom Hearts games' logos. They also have small blue bat-like wings on their back, gold-tipped feathered wings on their forearms, and bluish-purple fireballs under their feet, presumably assisting them in their fast movements and tying into their dark fire attack. Their long tails appear scaly, and end in a sharp, crescent-shaped blade.
Unlike many Heartless, which tend to attack with natural weapons like claws or magic-based powers, the Invisible bears a scalloped, blue-bladed sword, which appears blunt, but can unleash powerful physical blows. The kanji for "Hard Core" (硬核 Koukaku ) are written on the hilt of the blade.
The Heartless's name references its ability to disappear when using its "Ring of Fire" curse attack.
The Invisible fires dark energy every now and then, and uses its sword to slash at Sora. One of its special attacks includes throwing its sword in the ground, while the main body turns into a ring of dark fire surrounding either Sora, Donald, or Goofy. The ring of dark fire appears to circle the person closest to the Invisible. Once the time is up, the curse explodes, dealing large damage to any member of the party. This can be avoided by jumping, using Superglide, or using Dodge Roll. Like Angel Stars, they have a high rate of dropping a Gale once you've defeated them.
In Kingdom Hearts 358/2 Days, the Invisible can still perform its basic slash attack, but is given an "improved" arsenal of abilities from its Kingdom Hearts version. Its "Ring of Fire" attack is upgraded to cause its weapon to fly at Roxas up to five times while the beast is invisible, before surrounding Roxas with the ring and striking down with a long-range shockwave as a result. Striking the Invisible before it sends the shock waves will momentarily stun it. This Pureblood Heartless will fire a consecutive string of energy spheres, dealing a high amount of damage and possibly lowering Roxas's Defense to Lv. 1. It shares all of its abilities with its relative, the Orcus, a stronger and recolored version of the Invisible.