Anti-Riku is a dark version of Riku that appears in Kingdom Hearts 358/2 Days. It is fought in the Mission Mode version of Mission 93: Believe, replacing Riku at The World That Never Was. As it only appears in Mission Mode, Anti-Riku does not exist in Kingdom Hearts canon.
Anti-Riku, true to its name, is a doppelgänger of Riku as he appears in Kingdom Hearts 358/2 Days. Its entire body is black, as is the Oblivion Keyblade it wields.
Anti-Riku's name reflects the fact that it is an antagonistic, dark copy of Riku. The prefix "anti-" means "against".
Anti-Riku uses the same battle techniques as Riku. At the start of this battle, the player should immediately Lock-On to the boss. This should aid the player in keeping track of it, as Anti-Riku is fast. As soon as this is done, the player should attack Anti-Riku from the back. The player will not be able to deal damage if Anti-Riku is attacked from the front, as the boss will utilize Dark Shield and block them. A majority of this battle will be following Anti-Riku around the battlefield in front of Memory's Skyscraper.
When the player gets close to Anti-Riku, it will attempt a series of thrusts with the dark Oblivion Keyblade it wields. Anti-Riku may also launch a Dark Firaga attack if the player is not within close range. One can use proper timing of Guard to deflect this attack. When Anti-Riku's HP starts to diminish, it will begin to utilize a Dark Break-style desperation attack, which can be dodged via Dodge Roll or Glide. Just when Anti-Riku's HP is about to hit zero, it gains access to the Dark Aura ability. When using this attack, Anti-Riku will jet around the battle area, unleashing columns of black flame at the combo's end. The player can time this attack to when the boss's weapon begins to glow with a white-blue energy. It should be noted that blocking the lunging combos Anti-Riku uses before its blade glows will cause it to stagger, opening it to a brief combo. So long as one heals regularly and utilizes magic and one's Limit Break accordingly, Anti-Riku should fall relatively easily.