Odysseia Knights

The Odyssea Knights (also known as Odyssey) is an infamous guild whose members believe that by clocking enough deaths, an Adventurer would be able to return back to the real world. Despite their infamy, they are also known for helping out with quests and events, perhaps as a way to die without actually killing themselves.

Rogue Guard arc
Little is known about them, only being briefly mentioned by Henrietta during her analysis of the dangers roaming the Yamato server during the murderer's rampage.

Despite the guild's small size, it has gained a fearsome reputation due to the extremity of their beliefs. However, Henrietta temporarily overlooks it in favor of dealing with the rogue Royal Guard first, believing that it was too much for her to handle.

Route 43 arc
The Odyssea Knights are around Minami, and are seen when hundreds of Wyverns attack. Using their portable Shrine, they recklessly charge into battle, dying over and over, even killing each other in their madness, only to respawn at the shrine and charge right back in. Roe2 notes that they have become addicted to death, and surmises that the Genius' plan is being forwarded by their actions, while Minori and Tohya look on in horror.