Tied with Valkyrie for the world record! (I probably would have beaten it if Gilgamesh didn't start the round with Sloppy Swordplay...)

Build:

Cloud:
Rune Blade, Cetran Armlet, Chocoking's Cape
Magnify-Empowerment, MP Absorb-Lightning, Magic Focus-Lightning, Magnify-Lightning, ATB Stagger, Luck Up, Luck Up, Enemy Skill, ATK⟷MATK, Strength Up
Summon: Odin
Weapon Skills: Magic Attack +20, Enemy Parts Damage Up, Full-Power Magic, ATB Charge Rate Up

Aerith:
Ceremonial Staff, Cetran Bracer, Genji Gloves
Magnify-Fire, Swiftcast-Fire & Ice, MP Absorb-Fire, Magic Focus-Fire, ATB Stagger, Skill Master, Magic Up, First Strike, ATB Boost, Auto Unique Ability
Summon: Phoenix
Weapon Skills: Fire Damage Up, ATB Charge Rate Up, Magic Attack +20

Yuffie:
Fuma Shuriken, Hermes Shoes
Speed Up, First Strike, ATB Boost, ATB Assist, Elemental-Fire in armor
Summon: Gilgamesh
Weapon Skills: Weapon Ability ATB Recovery, ATB Charge Rate Up