No Heart is a simulated version of Xehanort wearing Keyblade Armor. It is an optional boss in Kingdom Hearts Birth by Sleep Final Mix that serves as the only enemy in the "Peering into Darkness" battle at the Mirage Arena.
Kingdom Hearts Birth by Sleep
No Heart wears a suit of Keyblade Armor. The Keyblade Armor itself is adorned with several Nobody emblems; one appears on the piece of armor covering No Heart's torso, two protrude from No Heart's greaves, and two more cover the boss's boots. No Heart's crown and shoulder pad are gold, while the rest of its Keyblade Armor is light blue and silver in coloration. No Heart wears two silver belts on its waist; instead of a spiked pauldron, white feathers cover its right shoulder. Several cords crisscross in front of No Heart's torso; these connect a pair of baggy sleeves to the massive, oblong pieces of armor No Heart wears on each arm. Before fighting, No Heart removes both of these sleeves, as well as the straps connected to them.
No Heart's faceplate is beak-like in structure; the boss wears clawed gauntlets, and black pants appear underneath its Keyblade Armor. No Name is No Heart's weapon of choice; the boss's Keyblade Armor shares its design with the armor worn by Xemnas in his Armored Controller form.
"No Heart" is an anagram of "Xehanort" with the "X" removed.
No Heart is a deadly opponent. It wields its Keyblade with deadly skill, able to Formchange it into various forms to attack and can even have its Keyblade float around on its own accord. It is deceptively agile, dashing across the battlefield to strike.
No Heart is also gifted in magic, being able to generate a shield and summon Keyblades from the Keyblade Graveyard to attack.