Traveler

The Travelers ( 航界種トラベラー ) are an artificial, non-corporeal race from the "third world" that arrived in Theldesia during the Eclipse&mdash;their name for the Catastrophe&mdash;just like the Adventurers. Split into two factions, the Fool-inspectors and Genius-collectors, their objective is to seek out and harvest Empathiom for their home world.

Overview
The members of this race did not have physical bodies to begin with, so they had to take bodies that already existed in Theldesia (either accounts that were inactive at the time of the Catastrophe or the bodies of monsters).

The Genius intend on focusing their efforts on destruction and chaos while gathering Empathiom (as their name suggests), while the Fools seem more interested in observing the other players as well as the physical sensations and experiences that Elder Tale has brought to them (likewise, as their name suggests).

They have a better understanding of the Catastrophe than the Adventures, however Roe2 admits they don't have a solution for it.

Before the Catastrophe
The Travelers are an artificial life form created in order to find Empathiom. The world that their creators came from ran out of Empathiom before they fully realized that creating Empathiom required a present source of it; as a result, the Travelers were created to search it out from different universes. They created something known as the "Backdoor," a mathematical phenomenon that would be used to find other universes with Empathiom. Using it, they were involved with the Catastrophe, knowing full well what would happen.

The universes are usually tied to several common rules. First, only one intelligent life form exists per universe. Second, the Law of Providence Horizon states that no two intelligent life forms can coexist in the same universe. Third, the Law of Contradiction dictated that before a contradiction could occur, one of the life forms would cease to exist. As a result, normally the Travelers' search would end in failure. However, the world of Theldesia was an exception as a result of the Catastrophe, which caused three forms of intelligent life to exist in the same universe. According to the Law of Providence Horizon, two of these three life forms should not exist here.

The Genius immediately began harvesting Empathiom when they arrived on Theldesia as a result of their orders, while most of the Fools are observing.

Route 43 arc
Touya's Party, while traveling in the Sakawa Region, encounters a group of People of the Earth facing a horde of Ogres when they hear a voice through the trees warning them of more higher level ogres being on the way. As the group is fighting the monsters, Roe2 appears out of the forest to join them in battle and summons a Princess Wraith to aid them in battle. She also formally introduces herself to the group and reveals that she is a vampire who is also travelling to the south in order to change her subclass, complaining that the person who chose it for her gave her a rather cumbersome one

She watches the invasion of Wyverns in the city of Saphir and the Odysseia Knights' repeated suicide tactics, which she believes to be part of the Genius plans, since it creates something called "Empathiom." Minori asks who Roe2 really is. She answers that she is a Traveler and gives a long explanation beyond anyone's comprehension. In the end, she joins the battle against the Wyverns.

After the battle she hands Minori a letter addressed to Shiroe.

Kanami, Go East arc
In China, Kanami's Party hears reports that the Lelang Wolf Cavalry was wiped out by undying monsters. Upon hearing this, Kanami decides to go face down these monsters, with Elias Hackblade and Coppelia following her. Although Leonardo initially hesitates, he agrees to go after talking with KR. The party is successful in killing the two Genius monsters they face, although KR is killed and sent back to Yamato in the process.

The Genius also have a secondary objective: to destroy any means for the Adventurers to reach Mare Tranquillitatis and communicate with the Fools, so anything they find that could make this happen is to be immediately destroyed, such as the abandoned space station in Tone's Grave in the Chinese server. Because the Lelang Wolf Cavalry went to intercept them, the Genius were also able to harvest Empathiom off of the Adventurers.

Later, it is revealed that KR joined Plant Hwyaden in order to gather more information about these monsters. From his research, the Genius were moving around the server and walking around, unseen and unknown. One is in Nakasu, while two are in Akiba.

Noosphere arc
Shiroe reads Roe2's letter, which was written while Touya's Party was in the Town of Saphir. The letter explained her circumstances, as well as her knowledge about the Travelers.

Other Media
In the Log Horizon TRPG Replay, the members of Nyanko-tei face and kill the Genius Monster called Sislau.

Fools Faction

 * Roe2
 * Tamasaburo (temporarily controlled by the Fool using Roe2's body)
 * Nantur (both a Fool and a Genius)

Genius Faction

 * Baglis
 * Bucaphi
 * Camaysar
 * Heiglot
 * Mascarun
 * Mizkun
 * Papus
 * Rasphuia
 * Sachluph
 * Sislau
 * Taliktan
 * Zahun

Related Terminology
Terminology related to the Travelers make heavy use of ruby characters. Ruby characters give a "proper reading" for the term, which is different from the kanji used to spell it and gives a single term multiple meanings. Because this is extremely difficult to translate into English, which lacks such a concept, this section is meant to better understand the various terms pertaining to the Travelers.

Backdoor (Fissure Prime)
The Backdoor, or the Fissure Prime, is a mathematical method used by the Holders to seek out other universes with sources of empathiom.

In Japanese, the term used is 素数亀裂バックドア. The kanji literally translates to "prime number" (素数) + "fissure" (亀裂), while the proper reading is "Backdoor" (バックドア). In computing, a backdoor refers to any method of bypassing normal authentication or encryption.

Eclipse
The third world's name for the Catastrophe.

In Japanese, the kanji used is 合致 (Pact), but the proper reading is エクリプス (Eclipse).

Fool
The Fool-inspectors (also called Fool-observers) are one of the two Traveler factions alongside the Genius-collectors.

Holders
The mysterious denizens of the third world who exhausted their world's supply of empathiom and created the Travelers to seek out and harvest it.

In Japanese, the term for them is 創造主ホルダー. The kanji reads "creator" (創造主) while the proper reading is "holder" (ホルダー).

Third World
The world from which the Travelers originate is called the "third world" (第三世界). Little is known about this world besides the fact that they use empathiom as a resource.