Xenoblade Chronicles 2 Blade Combo Elements

Fire -> Fire -> Fire
Fire -> Fire -> Light
Fire -> Water -> Fire
Fire -> Water -> Ice
Water -> Water -> Water
Water -> Water -> Dark
Water -> Earth -> Wind

Ice -> Water -> Wind
Ice -> Ice -> Earth
Ice -> Ice -> Dark
Wind -> Wind -> Earth
Wind -> Wind -> Electric
Wind -> Ice -> Ice

Electric -> Fire -> Wind
Electric -> Fire -> Ice
Electric -> Electric -> Water
Earth -> Fire -> Wind
Earth -> Fire -> Earth
Earth -> Earth -> Electric

Light -> Electric -> Fire
Light -> Light -> Water
Light -> Light -> Light
Dark -> Light -> Electric
Dark -> Dark -> Earth
Dark -> Dark -> Dark

Final element determines what gets "sealed" and also puts an elemental orb of that type on the enemy. The orb reduces damage from that element, and it can be destroyed for massive damage during a party chain:

Fire: Seal Self-Destruct
Water: Seal Stench
Ice: Seal Shackle Blade
Wind: Seal Blowdown
Electric: Seal Back Attack
Light: Seal Affinity Down
Dark: Seal Reinforcements