Sephiroth is the embodiment of Cloud's darkness. He is regarded as one of the most powerful villains in the Kingdom Hearts series, changing from an optional boss to a minor story character from Kingdom Hearts to Kingdom Hearts II. He, along with Cloud, Tifa, Aerith, Yuffie, Zack, and Cid, come originally from the Squaresoft game Final Fantasy VII, where he served as the main antagonist.
Sephiroth was designed by Tetsuya Nomura. Sephiroth, in all his appearances, wears a long black coat with silver pauldrons, black boots and black clothing. The top of his clothing underneath his uniform is split to reveal his chest, covered by crossing leather straps. Sephiroth's hair is long and silver, a contrast to Cloud's blond spikes, with his bangs parted to either side of his face. In Crisis Core -Final Fantasy VII-, his bangs are noticeably shorter than in any of his earlier appearances. Beyond his clothing and hair, Sephiroth is known for his green cat-like eyes and the Masamune, his seven-foot long katana he is rarely seen without. His battle stance with the sword is to hold it over his left shoulder with the blade curving downward. Sephiroth usually wields the Masamune two-handed. In later appearances a single black wing emerges from his right shoulder.
In the Compilation of Final Fantasy VII, Sephiroth's uniform remains the same as in Final Fantasy VII, but his coat has several buckles instead of just one, and the original SOLDIER logo in his belt is replaced with the redesigned version of the logo for the Compilation.
In the Kingdom Hearts series, Sephiroth retains his core design of silver hair and a black coat, but his clothing is given red linings and is a different shape. His sleeves have small red wings, and he bears a black wing over his right shoulder, which has become another of Sephiroth's trademark character traits. He bears two additional wings underneath his coat in Kingdom Hearts II. In Dissidia, Sephiroth's design is similar to his Final Fantasy VII design, but his pauldrons are changed to resemble Yoshitaka Amano's artwork and his coat is closed by a belt as in Nomura's design.
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, though 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 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. For some reason there is an odd, black and red, fin-like growth on his right forearm. Sephiroth's face looks strikingly like Cloud's, which is something that Goofy comments on in Kingdom Hearts II. This similarity would explain Sephiroth's difference in eye color from his original incarnation.
Sephiroth's chest is exposed, showing that he wears some sort of grey strap around his abdomen with two black belts over it, as well as two brown, overall-esque straps that intersect over his chest. He wears black pants and knee-high boots of the same color, with two grey belts wrapped around each boot. He wears a silver pauldron over each shoulder, both of which closely resemble the pauldrons he wears in the Compilation of Final Fantasy VII series. 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 sprouting from either of his hips. Also in both games, Sephiroth carries his iconic weapon, the Masamune (which is a katana with a massive length but thin width, making the sword resemble a Nodachi), as his weapon. Sephiroth is also one of only two characters who did not reappear in their Advent Children attire, the other being Cid.
Sephiroth's personality is one of cold ruthlessness. Prior to his madness, he was not particularly anti-social, as he has friends in Crisis Core -Final Fantasy VII- and willingly tells Zack and Tifa about Mako and Materia on Mt. Nibel. All the same, his cold exterior and professional attitude turn people away. Sephiroth is intelligent and respectful to those he deems worthy - he considers Professor Gast Faremis a great scientist, but looks down on Professor Hojo and describes him as "a walking mass of complexes". In Crisis Core Sephiroth maintains an outwardly professional demeanor, but is loyal and friendly to a select few, and has a dry sense of humor. Sephiroth is confident to the point of arrogance, but as the strongest SOLDIER alive, it could easily be argued he has the right to be. Well-spoken and somewhat graceful, Sephiroth is universally calm, collected, and in control. He can be frustrated and caught off his guard, but this rarely happens.
Following his fall into insanity, Sephiroth retains most of the above personality traits, but becomes murderous and vengeful. He also develops something of a messiah complex, proclaiming several times he is "the chosen one", destined to lead the Planet and become a god. In Dissidia Final Fantasy, Kefka calls him "Just another sadist with a god complex. Like THAT'S anything special!". His intelligence has increased vastly following his time in the Lifestream where he absorbed the knowledge of the Ancients. At one point, Sephiroth even says he is greater than the Ancients. He has become highly cruel and delights in mentally torturing Cloud, and in Advent Children, in one of his iconic lines, asks Cloud what he cherishes so he may simply take it from him. Sephiroth is fiercely devoted to Jenova and her cause, even though her body serves as little more than his avatar. However, it is also stated that he himself is an agent towards Jenova's will.
Interestingly, in Dissidia, there was at least one hint that he may have some sadness despite his nature, as Cecil Harvey tells Sephiroth before fighting him that "there is sorrow in [Sephiroth's] wintery eyes."
In the Japanese releases, Sephiroth uses the pronoun "ore" prior to his insanity, a common masculine pronoun. Following his "death" at Nibelheim he begins to use "watashi" instead, a more formal pronoun with no attached gender. This post-madness mannerism is also used in his spin-off appearances such as Dissidia.
Even after appearing in so many titles, Sephiroth's true power is unknown. It's stated in the official book Reunion Files the Sephiroth seen in Advent Children has "ascended to a new level of existence" and is much stronger than before. Though he was defeated, Sephiroth never used the full extent of his powers in the final fight against Cloud, and because of that his true potential is still unknown. Advent Children producer Yoshinori Kitase has said "Sephiroth's existence and will is extremely powerful. There is nothing stronger, nothing above him."
Sephiroth is a master swordsman and has superhuman strength, agility and reflexes. He is able to produce beams of energy by swinging his sword, dash past or up to opponents in the blink of an eye, and can effortlessly cut through solid metal and concrete with his signature weapon, the Masamune. He has great magical abilities, and is equipped with a full set of Mastered Materia in Final Fantasy VII. In Crisis Core he is able to teleport, the only Final Fantasy game where he can do this, but he also has this ability in the Kingdom Hearts series. Zack Fair, Genesis Rhapsodos, Elfé, Lightning, and the Warrior of Light have been able to battle Sephiroth competently, but none have actually defeated him at his full potential - he eventually overpowers Zack, Genesis and Elfé, and is it implied he was holding back when facing Lightning and the Warrior of Light. Only Cloud has shown the consistent ability to best Sephiroth in battle across his various appearances.
Following his immersion in the Lifestream Sephiroth gains the ability use magic without the need for Materia, and can manifest the Masamune from the Lifestream by willing it to appear. Having taken over Jenova he is able to shapeshift her cells into his visage and other forms. This allows Sephiroth to remain "alive" in a sense even when dead by morphing Jenova's cells into a new body for himself to act through from within the Lifestream, but his ability to do this seems limited. Sephiroth also has a measure of psychic abilities, able to read minds, project illusions, and levitate objects and people. As an extension of his control over Jenova, Sephiroth is able to control the "negative Lifestream" composed of those killed by Geostigma, as shown in Advent Children. In Advent Children Sephiroth has the ability to fly, and in his EX Mode in Dissidia has the ability to glide using his wing.
Sephiroth's trademark attack is Supernova, his ultimate attack when faced as Safer∙Sephiroth. Crisis Core and Dissidia present Supernova as his Limit Break. Sephiroth's other trademark attacks are Heartless Angel, a move that drains the opponent's HP to a single point, Octaslash, a sequence of eight sword attacks, and Shadow Flare, a barrage of dark energy orbs. In Kingdom Hearts and Dissidia, he is also able to use Meteor.
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 drove him to insanity. Easily recognizable by his foreboding appearance and frighteningly long sword, Sephiroth aspired 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. Constantly impeded by Cloud Strife, Sephiroth has seemingly grown a murderous obsession with him.
Almost all of Sephiroth's attacks, such as "Super Nova", "Heartless Angel", and "Shadow Flare", are named for 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 for attacks in the series. Sephiroth's "Heartless Angel" technique was originally first used by the Final Fantasy VI primary antagonist, Kefka Palazzo. It would later reappear as an attack of his in Crisis Core: Final Fantasy VII. Some of Sephiroth's moves from the Kingdom Hearts series have been seen in use the crossover fighting game Dissidia Final Fantasy as well as Crisis Core: Final Fantasy VII, due to the circumstances and limitations concerning the original Final Fantasy VII. Such attacks have made an appearance such as the Reaction attack used by him in the latter game, as well as manifesting darkness orbs and teleporting. The Meteor spell from both Kingdom Hearts II and Dissidia Final Fantasy involve a glow of sorts, and the Heartless Angel both show feather-shedding. In the North American version of Dissidia Final Fantasy, he is seen using the pop-up attack from Kingdom Hearts II.
Sephiroth's persona is one of cold ruthlessness. He is uncaring, having no sympathy for anyone but himself, laughing and grinning at Cloud, seeing him as almost no threat. Like many Final Fantasy characters, Sephiroth has been shown with stoic and melancholy personality traits, along with a drawling voice. He is incredibly powerful, both physically and mentally. He is convinced his power surpasses anyone else's. He is shown to have no emotion, never overreacting to anything.