Players seeking Sephiroth's Vision in Final Fantasy Resonance must first overcome the game's optional boss encounter. The Vision appears in the menu as a locked entry, inaccessible until the player defeats Sephiroth in battle. The encounter occurs after obtaining the airship in Chapter 5, when players navigate to a whirlpool north of the bridge leading to the desert in Grandshelt. Entering the whirlpool triggers a prompt to engage the boss.

The fight consists of three distinct phases. Sephiroth begins with approximately 250,000 HP at level 45, though players are advised to reach a higher level before attempting the battle. In Phase 1, he alternates between physical attacks, dark physical damage, and magic spells while blocking physical strikes with a counter ability. Phase 2 begins when his HP drops to 200,000, triggering immunity to damage during a transition period. Upon regaining vulnerability, he casts One-Winged Angel, followed by Heartless Angel, which reduces the entire party's HP to one. This phase requires a tank equipped with the Warrior of Light Vision to activate Multi-Cover, redirecting all incoming damage to the tank while the rest of the party remains at one HP. Elemental weaknesses shift during this phase; Sephiroth becomes vulnerable to the opposite element of his current infusion, and using non-elemental attacks risks triggering additional area-of-effect magic.

Phase 3 activates at 50,000 HP, where Sephiroth becomes immune to damage during a transition, then casts Divine Proclamation, placing a countdown meteor icon that ends the battle if it reaches zero. At this stage, he absorbs dark damage and gains a definitive weakness to light, making non-dark attacks essential for progression. Strategic use of Libra to monitor HP and weaknesses, combined with abilities like Mechamog Scan to implant permanent weaknesses, is recommended. Players should avoid over-reliance on buffs, as Sephiroth may cast Nihilistic Solitude to remove them and deal dark damage, which the tank can mitigate with Multi-Cover and Warrior of Light immunity.

Success hinges on preparation: equipping non-elemental Espers such as Odin or Bahamut, using Lid's Mechamog Scan early, and ensuring a dedicated healer with Firion's Arms Akimbo Mastery Skill at level 9. Healing Rain to sustain the tank and managing turn order to prevent consecutive attacks from overwhelming the party are also critical.

Upon defeat, Sephiroth's Vision becomes available, granting access to his suite of abilities. His Resonance skill, True Octaslash, delivers non-elemental physical damage to all enemies eight times, each hit potentially critting when paired with Ultimate Aggression mastery. His skill list includes Boundless Void, Dark Surge, and Meteor, alongside mastery bonuses that enhance critical hit rates, damage output, and HP recovery. While his Vision offers significant offensive utility, unlocking it demands a well-structured strategy, appropriate gear, and multiple attempts to navigate the fight's escalating challenges.