Sephiroth begins the fight by casting Firaga. Afterwards, he will use his normal pattern of attacks with his Masamune: he will perform powerful combos and uses Telluric Fury, Aerial Onslaught and Scintillia as his special sword moves. All can deal considerable damage and Sephiroth can also deflect attacks with the Masamune, either being immune or reducing the damage. He will continue to cast Firaga and sometimes use Blizzaga. Cloud can either stagger and then fling him to another piece of a building, or he will be sent flying to another building. This will continue until Sephiroth has taken enough damage, after which he will fling Cloud away and another party member will join him, beginning the second phase, which Sephiroth will start by casting Aeroga.
Sephiroth will begin using Thundaga and Boundless Void, which paralyzes Cloud for Sephiroth to deal a powerful 2-hit combo. His most dangerous attack is Hell's Gate, which can reach vast distances and hit both Cloud and the other party member. In Hard mode, Sephiroth will have Masamune In Waiting, which could block any incoming damage. Cloud and another party member can either stagger and then send Sephiroth crashing down, or Sephiroth will collapse the building they are fighting on with Hell's Gate and simultaneously deal damage. After Sephiroth takes enough damage, he will manifest his wing and use Gravity on Cloud and the other party member, only to be saved by a third party member.
At the third phase, Sephiroth will use Elemental Infusion, and apart from the similar increase in the power of his elemental spells and absorption of the elements he infuses himself with, the abilities he gains vary for each element, and his fighting style changes with each Infusion:
- Fire Infusion grants him Flamewall, creating a wall of fire that lasts for a considerable amount of time and damages any party member close. As Sephiroth can teleport, he is unbothered by the flame wall, and will attack aggressively.
- Lightning Infusion grants him Thunderstorm, calling down multiple powerful bolts of lightning. Sephiroth prefers his ranged energy slashes, chaining thunder strikes soon after.
- Ice Infusion grants Sephiroth Frostpike, summoning multiple chunks of ice on the battlefield called Frostbite and will explode with enough time. He prefers to use ranged beam attacks, Blizzaga, and Hell Gate.
- Wind Infusion grants Sephiroth Windmail, which causes his sword strikes to be accompanied by numerous secondary strikes that while dealing small damage, can prove devastating combined with its original unhindered attack power. His Aeroga will also gain homing capabilities and will last longer than his regular Aeroga.
Before each Elemental Infusion, Sephiroth will use Octaslash, his most devastating physical attack, and the only way to prevent this is to stagger him, which can only be done by using the opposite magical element to the element he infused himself with. In time, he will cast a dark version of Elemental Infusion and in addition to being able to cast all the ga-level spells without any need of preparation, gains Shadow Flare, which creates a globe of dark energy that pulls the party in and explodes.
When close to death, Sephiroth summons a ball of fire from the sky. He will remain suspended and no longer attacks with the Masamune, but will cast Shadow Flare and Heartless Angel: Shadow Flare is enhanced to summon multiple gravitational orbs of darkness that pull the player in and explode, and Heartless Angel has Sephiroth throw his sword and manifest a red field of energy and black feathers that greatly reduce the player's health. Sephiroth will also use dark-energy attacks: When high in the air, he will fire multiple dark feathers but if he is on the ground, he will fire dark energy projectiles capable of paralyzing and dealing constant damage to you. He can also perform a strong dark-energy slice that will reach until the end of the arena he attacks and if he slams his sword into the ground, he'll create a dark air that will damage and repel any party member close. Sephiroth must be defeated before the count reaches zero, or else he will use Divine Proclamation and launch another "Supernova," instantly killing the party.
When the battle begins, only Cloud is available. As it progresses, two more party members will join him but are chosen at random. For this reason it is important to keep all characters battle ready in the event they are the ones who join the battle.
By using Elemental Materia combined with either Fire or Ice Materia in an armor can make Cloud resistant or even immune to either element, which can help considerably. However, Sephiroth will resist all elements later, and thus using elemental magic will not deal significant damage on him. To make staggering easier, the player should block Telluric Fury with Punisher Mode active, as this will considerably reduce damage, and also pressure Sephiroth, making him wide open to attack with Strong Attack. It is best to not damage him when Scintilla is active, as Sephiroth will counter it with heavy damage. The player should keep blocking with Operator Mode against the element Cloud is not immune against. If the player manages to stagger Sephiroth, he will then start using Aolian Onslaught, which is hard to counter with Punisher Mode. Staggering Sephiroth twice will make Hell's Gate available to him.
After enough damage is inflicted, another party member will join. The player should keep attacking and blocking Sephiroth's attacks, and stagger him to advance. When enough damage is dealt, he summons his dark angelic wing (a nod to "One-Winged Angel," which starts playing in the background). A third party member joins next.
In the next phase, Sephiroth becomes much more dangerous. The idea here is to get him pressured quickly. He attacks relentlessly with elements, depending which Infusion is active. This makes him vulnerable to the opposing element, so the player can use them to their advance: Ice against Fire and vice versa, Lightning against Wind and vice versa. Aerith is usually the most powerful magic user, and she can use a spell twice in succession with Arcane Ward. Sephiroth uses a fixed pattern of attacks. If the player can't pressure him before the pattern ends, he will unleash Octaslash, which is his most dangerous ability in this phase. After Octaslash, he uses different infusion, and restarts the pattern.
Once enough damage is inflicted, the final phase begins. Sephiroth must be defeated before his countdown reaches zero. At first, he uses Shadow Flare. The player should avoid them by evading, then attack while remaining mindful about their positioning, especially when Sephiroth launches his signature ability, Heartless Angel. Heartless Angel affects a wide area, and anyone inside will have their HP reduced to 1.