The Guardian Knights (守護騎士, Shugo Kishi?) are the guardians of the World Tree in ALfheim Online, whose purpose is to prevent anyone from reaching the top of the Tree. They use swords, spears, and bows and arrows to fight players.
Their attack strategies include direct sword attacks, as well as being able to throw their sword-like shooting spears and attacking in large groups, while other Knights, which are equipped with bows and arrows, fire arrows at the players from long range.
When someone accepts the Grand Quest challenge, they must get past a whole army of them before they can complete the challenge by reaching the top of the tree. Guardian Knights not only spawn in immensely large numbers, but also immediately re-spawn when killed. They also have an irregular targeting pattern: unlike most monsters, Guardian Knights are shown to target players performing supportive roles while disregarding the main attackers.
- It was stated by Yui that the Guardian Knight's stats actually aren't very high. However, they always come in overwhelming numbers, outnumbering the players and spawning at a rate faster than they can be killed, thus making it impossible to beat them. Kirito also describes them as a "single, unbeatable boss".
- Unofficially, the first Grand Quest cannot actually be beaten even if the player does manage to get past the guardians, as the gate leading to the upper levels of Yggdrasil requires administrator access to open, thus regular players are unable to open the gate.