Spoiler Alert: This article or section contains details about plotlines not covered in the anime. Do not proceed unless you wish to be spoiled.
The Elf War (エルフ戦争,Erufu Sensou?) is the first campaign quest in Sword Art Online, spanning numerous chapters that take place from the 3rd Floor of Aincrad to the 9th Floor of Aincrad. At the beginning of the quest, the players must choose to either support the forest elves or the dark elves, thus branching the campaign into two main paths with different quests. The campaign quest plays a prominent role in the Progressive Arc.
The players encounter a forest elf battling against a dark elf in the Forest of Wavering Mists. The player must choose one of the elves to support and either kill the other elf or wait for their elf to use a last resort attack to kill themselves and the other elf once the players' hit points reach the yellow zone. The players must then return the Jade Key the elves were carrying to either the forest elf base or dark elf base respectively.
Vanquishing the Spiders (毒蜘蛛討伐,Dokugumo Doubatsu?)
The dark elf commander requests the players to find the nest of poisonous spiders that were sabotaging patrol missions. The first part of the quest requires the player to find the corpse of a dark elf scout on the first floor of the nest and bringing a leaf-design emblem from the scout to the dark elf commander. The second part of the quest involves killing Nephila Regina, the queen spider of the nest, and then bringing the Queen Spider's Poison Fang to the dark elf commander.
The scout is revealed to be a forest elf using a disguise charm who attempts to steal the Jade Key. The players form a temporary party with Dark Elven Wolfhandlers to follow the imposter scout’s tracks to a large forest elf camp.