Sephiroth

Sephiroth is a mysterious swordsman with a connection to Cloud's past. Cloud considers Sephiroth a representation of his own inner darkness. He, along with Cloud, Tifa, Aerith, Yuffie, Zack, and Cid, originates from the Squaresoft game Final Fantasy VII, where he serves as the main antagonist. So far, Sephiroth is the only main antagonist from the Final Fantasy franchise to appear in the Kingdom Hearts series.

Development
Sephiroth originally appeared as an optional boss in the international version of Kingdom Hearts, and was retained for the Kingdom Hearts Final Mix version of the game, which also added a short scene between him and Cloud. In Kingdom Hearts II, his role was greatly expanded, giving him a short side-story featuring him, Cloud, and Tifa.

Kingdom Hearts Unchained χ
In the cinematic for Quest No. 333, "The Final Trial Pt. 8," a black feather falls in Cloud's hands at the Underworld Caverns: Depths. It's implied that Cloud is searching for Sephiroth, explaining why he willingly went to the Underworld and escaped as soon as he gathered the feather.

Sephiroth also appears as a medal.

Kingdom Hearts Birth by Sleep
While Terra is in Olympus Coliseum, Zack reveals that he aspires to become a hero like "another," referring to Sephiroth. Later, after Master Xehanort's defeat, a black feather falls before Zack as he watches Hercules train, hinting at Sephiroth's presence.

Kingdom Hearts
Sephiroth appears during the Platinum Match at Olympus Coliseum, and after a difficult fight, Sora narrowly seizes victory. As Sora leaves the stadium, Cloud enters. Sephiroth invites Cloud to turn to the darkness, but Cloud refuses, launching into a high-speed aerial battle whose outcome is left unobserved.

Kingdom Hearts II
Right before the invasion of Hollow Bastion, Cloud warns Sora and company about Sephiroth, and his ways of the darkness. Later, as Sora exits the castle to help defend against the invasion, Sephiroth appears. He asks about Cloud's whereabouts, and although Sora says nothing, Donald and Goofy retort that Cloud recognizes Sephiroth to be the manifestation of his own darkness. Seeing that Cloud is becoming enlightened and desiring to fight him, Sephiroth takes his leave.

During the battle, Cloud is surrounded by Heartless, but Sephiroth intervenes, defeating them all in one slash. Cloud intends to defeat his nemesis to escape the darkness, but Sephiroth only replies that Cloud would never be able to do so, and would always cower in the light. Cloud vehemently denies his dark counterpart's claims, but Sephiroth is undeterred, and leaves just as Tifa arrives.

After the Master Control Program is defeated, Sora encounters Sephiroth at the Dark Depths at Hollow Bastion. The villain again asks about Cloud, but Sora and his companions do not reveal anything. He then inquires about Sora, Donald, and Goofy's identities, but again, they refuse to answer. Sephiroth then notices Sora's Keyblade and attacks, intending to test Sora's power and that of the Keyblade. Even though Donald and Goofy accompany Sora when he confronts Sephiroth, they do not fight alongside him, as Sephiroth only wishes to battle the Keyblade master. Sora appears to overcome him, but Sephiroth simply shrugs off the battle. Sephiroth compliments Sora on his skill in wielding the Keyblade, but says that Cloud is the only one that could "eliminate him." Sephiroth then tells Sora to find Cloud so that they could settle their feud.

Cloud arrives later, and initiates a battle with Sephiroth, who desires to draw Cloud into the darkness. However, Tifa protects Cloud, saying that Cloud does have light in him, and that, even if he didn't, then he just needed to be surrounded by light. Nevertheless, Sephiroth and Cloud start off for another battle, and after Tifa's intervention, Cloud glows in light, surprising Sephiroth and causing him to drop his guard. The two disappear in a brilliant flash of light.

Appearance
Sephiroth's appearance in both Kingdom Hearts and Kingdom Hearts II is largely the same as his appearance in the various games of the Compilation of Final Fantasy VII, albeit with a few significant differences. He has his distinctive long, silver hair with long bangs that frame his face, and dresses in a black leather coat. The coat has a large collar that reaches his ears even when folded back, and is kept closed by a black belt with a silver buckle around his waist. Unlike in the Final Fantasy games, Sephiroth's coat has a red-violet lining in the front. It is also noticeably more tattered in the Kingdom Hearts games. In Kingdom Hearts, Sephiroth also has regular blue eyes, unlike the green, catlike eyes he and his Remnants have in the main series. The sleeves of his coat end in metal rings in place of normal cuffs, and he wears black leather gloves. There is an odd, black and red, fin-like growth on his right forearm. Sephiroth's face looks strikingly like Cloud's, which Goofy comments on in Kingdom Hearts II. This similarity may explain Sephiroth's difference in eye color from his original incarnation.

Sephiroth's chest is exposed, revealing a grey strap around his abdomen with two black belts over it, as well as two brown, overall-like straps that intersect over his chest. He wears black pants and black knee-high boots, with two grey belts wrapped around each boot. His eyes are blue, and he wears a silver pauldron over each shoulder. In both games, Sephiroth sports a large, navy blue wing on his right shoulder, a design feature that has carried over to several characters associated with Jenova in the Compilation of Final Fantasy VII. In Kingdom Hearts II, he gains two more wings of the same color, one of which sprouts from each of his hips. Sephiroth carries his iconic sword, Masamune, as his weapon. Sephiroth is one of only two characters who does not reappear in their Advent Children attire, the other being Cid.

Personality
Sephiroth is cold, calculating, and ruthless, though not entirely uncaring. He is taciturn and focused, determined to draw Cloud down the path of darkness. Like many Final Fantasy characters, Sephiroth displays stoic personality traits, coupled with an almost monotone voice. Almost emotionless, he never overreacts to anything. Sephiroth is incredibly powerful, both physically and mentally, and is convinced that his power surpasses that of anyone else. However, he is not as arrogant as others who had fallen to the darkness, such as Maleficent and Jafar, but gauges his opponents and admits their skill when they prove it, as he does at the end of his battle with Sora in Kingdom Hearts II.

Abilities
In all incarnations, Sephiroth is portrayed as a master swordsman, wielding a long blade known as the Masamune. In the Kingdom Hearts universe, Sephiroth boasts a large repertoire of techniques which reflect some of the abilities he used in Final Fantasy VII. He moves about with impressive speed, and is able fly and teleport. His "Firaga Wall" attack summons gigantic pillars of flames that can suck matter in. Another attack sends out orbs of darkness called "Shadow Flares". His most powerful attack, "Meteor," calls down meteors that revolve around him before exploding.

His most noticeable technique is "Heartless Angel", which that drains Sora's MP and kills him instantly (unless Second Chance is equipped, in which case he will be left with 1 HP), if he is not interrupted in time, immediately followed by "Flash", which is fatal unless blocked via Reaction Command. He also uses a variation of Cloud's "Omnislash", in which he flies around the arena slashing wildly. In both games, all of his attacks are extremely powerful, able to easily kill Sora even with maxed stats. Sephiroth has extremely high HP in both games. To add to the difficulty, Sora must to fight Sephiroth one-on-one without any help from his allies.

In Kingdom Hearts, Sephiroth ranks as one of the hardest bosses in the game, rivaling Kurt Zisa and Phantom, but is arguably surpassed in difficulty by Xemnas, known at the time as "Unknown". In Kingdom Hearts II, he is also one of the hardest bosses, but is again surpassed by the Organization XIII Replica Data and the Lingering Will.

Origin
Sephiroth debuted as the main antagonist in Final Fantasy VII. Once revered as a great hero, his discovery of the mysteries surrounding his origins and nature drives him to insanity. Easily recognizable by his foreboding appearance and frighteningly long sword, Sephiroth aspires to become a supreme being by using a destructive item known as the Black Materia to cast Meteor and devastate the world, wherein he would absorb the energy used to heal the Planet, and attain godhood. Sephiroth has developed a murderous obsession with Cloud Strife, who constantly impedes him.

Almost all of Sephiroth's attacks in the Kingdom Hearts series, such as "Supernova", "Heartless Angel", and "Shadow Flare", are named after attacks he uses in the Final Fantasy series. The few attacks he does not know in the Final Fantasy series, such as "Meteor" and "Flash", are still named after attacks in the series. Sephiroth's Kingdom Hearts appearance heavily influences his attacks in Dissidia Final Fantasy, such as his Flash attack from Kingdom Hearts II appearing as "Oblivion", and his Shadow Flare, which uses similar graphics to the two Kingdom Hearts games in the original Japanese version of Dissidia. His Heaven's Light HP attack resembles his aerial combo in Kingdom Hearts II, and in his EX Mode, Sephiroth takes on a purple aura similar to that he takes on in the Kingdom Hearts series when his HP is low. Sephiroth also quotes or paraphrases many of his Kingdom Hearts lines, such as "It's time" (based on "The time has come") and "Know your place."