Darkside

The Darkside is a Pureblood Heartless that is found in all Kingdom Hearts games. It is one of the bosses at the Awakening, Destiny Islands, End of the World, and Twilight Town. Its theme song is "Destiny's Force," which plays during each of its encounters, excepting its appearance in Kingdom Hearts: Chain of Memories, in which "Struggle Away" is played.

Kingdom Hearts Birth by Sleep
In the ending of Kingdom Hearts Birth by Sleep, Aqua is seen wandering the Realm of Darkness. A Darkside rises before her, several more appearing around her. Aqua summons Master Eraqus's Keyblade, but loses hope and decides to let the darkness consume her. As the Darksides prepare to attack, two shimmering lights destroy them, closer examination showing the lights to be Terra and Ventus's Keyblades, Earth Shaker and Fresh Breeze. Aqua then looks on as the Keyblades disappear from sight.

Kingdom Hearts
As Sora progressed through the Awakening, his shadow eventually grew into the Darkside. The Heartless later attacked the Destiny Islands after the Door to Darkness was opened, later being sucked up into a dark cloud that loomed above the islands, Sora sucked up along with it and transported to Traverse Town. A Darkside later rose up from the ground below and interfered with the battle between Sora and Xehanort's Heartless at End of the World. Sora also glimpsed a number of Darksides within the Door to Darkness before they were destroyed by King Mickey.

Kingdom Hearts 358/2 Days
The Darkside is fought in Twilight Town (during a mission involving Roxas and Xion) in Kingdom Hearts 358/2 Days. After Roxas depleted its HP, he found himself strangely weakened, his Keyblade knocked from his grasp. The blade reappeared in Xion's hands, Xion destroying the massive Heartless in a single strike.

Kingdom Hearts: Chain of Memories
In Kingdom Hearts: Chain of Memories, Sora fights the Darkside in the card world Destiny Islands, the Heartless appearing in a way very similar as it did in the first Kingdom Hearts. When Riku enters the card world, he too faces it, Zexion creating a replica of Riku and transforming it into the Darkside to show Riku what he "truly was."

Kingdom Hearts II
A Darkside appears in Roxas's dreams of Sora's memories.

Kingdom Hearts coded
A data version of the Darkside appears in Kingdom Hearts coded, which is battled by the Data Sora.

Kingdom Hearts
Darkside is an easy-medium boss, and you can defeat it very quickly. Its weaknesses are its head and hands. Its attacks in all three battles of Kingdom Hearts are:
 * Darkside punches the ground, causing a dark pool and mild shockwave to form. This attack gives birth to a small number of Shadows.
 * Darkside scoops up an orb of darkness, which splits into many smaller orbs that rain from the sky.
 * Darkside creates a dark force in the heart-shaped hole in its body, which shoots homing dark missiles. These can be dodged by standing behind the massive Heartless, or reflected back at the Darkside for major damage.

This is simply a hack-and-slash battle, with no real strategy needed. Simply attack at every opportunity and avoid Darkside's attacks. If you get low on health, defeat the Shadows it spawns as they drop HP orbs, or Cure. If you can climb Darkside's arm and attack its head, you get tech points for every combo finisher landed.

Kingdom Hearts: Chain of Memories
This memory-based incarnation of the Darkside utilizes the same tactics as its Kingdom Hearts counterpart, Card Breaks an easy way to avoid damage. Again the player must attack the arms to deal damage, Sora having to jump in order for this to be done. If a Gimmick Card appears, a plank of driftwood will appear that Sora can hop upon and float up to the Darkside's head on to deal extra damage. A combination of high-numbered Attack Cards as well as Cure Cards are recommended.

This strategy holds simlar to Riku's battle with the Darkside. Riku can utilize Dark Mode, Dark Firaga the most reliable Sleight in his arsenal, considering he only has two, Dark Firaga and Dark Break. Dark Break can be used more commonly, but it will often miss. It does have a tendency to hit the head, however. It should be noted that Sleights should not be abused by either Sora or Riku, as missing with them wastes much-needed cards, and the player will eventually run out.

This strategy can be used in Kingdom Hearts Re:Chain of Memories, the only difference being the Gimmick Card causes large plateaus to spawn.

Kingdom Hearts 358/2 Days
In Kingdom Hearts 358/2 Days, Roxas is also faced with the Darkside, having Xion as a partner. Xion will mainly cast Fire spells from a distance, so focus on attacking the Heartless's hands. It utilizes all techniques from past encounters, the same tactics able to be used in order to prevent most damage. The same strategies can be used, but it is advised that the player Jump as much as possible to avoid the Darkside's devastating long-range shockwave attack, used after many of its tactics. Roxas should also be in constant motion to avoid the energy that rains down, using Block to deflect the energy balls back at the boss. This battle should not be too much of a difficulty.

Its attacks always follow a pattern, starting with summoning the Shadows and ending with the dark balls falling from the sky. The pattern goes on until it is defeated.

Trivia

 * The Darkside battle shares many similarities with Twilight Thorn, a gigantic Nobody. Both appear in Roxas and Sora's Awakenings, respectively, and are the first bosses of the game. Their Japanese names, Twilight Zone and Darkside, are both science-fiction horror serials.
 * In Kingdom Hearts, Darkside had a flap of skin where the heart on his body creases at the top. In Kingdom Hearts Re:Chain of Memories this flap of skin was removed for unknown reasons.
 * The first Darkside battle is the only boss battle in the series in which Sora doesn't speak.
 * The Darkside battle in Kingdom Hearts is the only true boss battle in which Sora fights with a weapon other than a Keyblade.