Dark Aura

Dark Aura (ダークオーラ) is an ability primarily used by Riku throughout the Kingdom Hearts series. In most instances, Dark Aura consists of Riku jetting across the battlefield at high speeds out of portals of darkness to deal heavy damage to his opponents in rapid succession, concluding the devastating attack by plunging his weapon into the ground, spawning several columns of light. However, there is a variation of Dark Aura exclusive to Kingdom Hearts II, in which Riku merely fires spheres of dark flame at the opponent, a technique visually similar to Dark Firaga.

Mechanics
In Kingdom Hearts: Chain of Memories, Dark Aura is an attack sleight that Riku can use while in Dark Mode. The columns of flame that conclude the attack may enemies when hit. The card combination for Dark Aura is:

In Kingdom Hearts II, Dark Aura is an action ability that can be equipped to Riku once he joins the party in The World That Never Was. So long as Riku is in the active party, whenever Sora concludes one of his physical combos, the player can press to execute the Dark Aura Reaction Command, in which Riku fires spheres of dark flame at the opponent. Dark Aura can stop enemies on contact, and it costs two AP to equip and ten MP to use. During the final battle with Xemnas when the player is forced to play as Riku, Dark Aura can be used by pressing.

In Kingdom Hearts 3D: Dream Drop Distance, Dark Aura is an exclusive to Riku that uses two slots. It has a reload time of 42 seconds.

Kingdom Hearts: Chain of Memories

 * Riku learns Dark Aura once he obtains the ability to enter Dark Mode.

Kingdom Hearts II

 * Riku has Dark Aura as a default ability.

Kingdom Hearts 3D: Dream Drop Distance

 * The Ghostabocky has Dark Aura in its Ability Link.
 * The Keeba Tiger has Dark Aura in its Ability Link.

Other appearances
Riku is fought several times as a boss throughout the Kingdom Hearts series. Dark Aura serves as one of his desperation attacks in each of these encounters.

Kingdom Hearts
When Sora faces Riku for the second time while Riku is under the possession of Ansem, Seeker of Darkness in Hollow Bastion, Dark Aura serves as Riku's strongest attack. It is used when he is low on HP and his hand is glowing in a sphere of dark energy.

Kingdom Hearts: Chain of Memories
As a Replica created from the real Riku's combat data, the Riku Replica can utilize all of Riku's abilities which are exclusive to Dark Mode. Unlike Riku, who needs a card value of 27 to execute Dark Aura, the Riku Replica can use it with any value, granted he only gains access to the Sleight during his final battle with Sora in the main story and Riku in Reverse/Rebirth.

The finale attack of Riku Replica's Dark Aura is about twice the range of what the real Dark Riku can actually use.

Kingdom Hearts 358/2 Days
During his battle with Roxas in The World That Never Was, Riku is able to use Dark Aura once he is low on HP. In Mission Mode, Anti-Riku can use Dark Aura as well.

Kingdom Hearts: Re:coded
Data-Riku can use Dark Aura at any time during the final phase of his battle against Data-Sora in Hollow Bastion.