Magus

Magus is a Human Sorcerer-Alchemist that instigates the bout of Player Killing and enslavement of weaker Adventurers by Hamelin, although he does not belong to the guild itself. He originated from Log Horizon: West Wind Brigade

He is really a girl trapped in a male avatar, similar to Akatsuki's initial situation.

Appearance
Magus resembles Shiroe, but has blank, psychotic eyes, especially prior to his change of heart. He has pointy, unruly, auburn-colored hair and wears a long collared jacket over his clothes.

After taking an Full Appearance Reset potion, Magus takes a female body. Her hair grows longer, and she dons a Gothic-lolita styled dress, although the dress still fits underneath her old jacket.

Personality
Magus appears to be a sadistic twisted person who loves to see other players suffer and die by Player Killing. He seems to be enjoying murder despite not doing the dirty work, although the plans he formulates are rather successful. The reason why he instigated PKing is because he dreamed of a world were people would fight, against other players, dangerous monsters, pitting blade against blade in battle, and sought to instigate that through PK.

He adamantly continued to view the world as a game, which is why he wanted to make things "like they were before".

Log Horizon: West Wind Brigade
Magus first appears when Isami confronts two Hamelin guild members, who are trying to force Tohya and Minori into joining. Under the guise of trying to help the two newer players, he successfully deflects Isami's suspicion and recruits the two children. However, after Isami leaves, it turns out that he incited the two Hamelin members to attempt to rape Isami and Sara. Although it fails, the subsequent fight involving Soujiro and a Royal Guard causes the first death in Akiba and reveals the immortality of the players, resulting in the drastic rise of Player Killing.

During Canossa's retreat after encountering the West Wind Brigade, Magus, Passhita, and Coza meet up with them in the forest. Magus asks them whether the PK was going well, and sounds delighted to hear about what the guilds have been doing. Canossa then gives Passhita some of the loot as one member asks Magus why they were PKing to receive EXP Pots rather than giving him gold. Magus simply responds that he needed an instigator, much to the confusion of the others. When the West Wind Brigade realizes about the rise of PK, Soujiro, Nazuna, and Isami end up confronting Magus, where Soujiro attempts to take down Magus only to discover that Minori and Tohya were being held hostage. Unable to do anything, Soujiro lets Magus go, apologizing to Minori for being unable to save them. Afterwards, Magus goes alone to a cave, delivering EXP Pots to Isaac.

After being defeated by West Wind Brigade and amending his ways, he obtained an Appearance Reset Potion through unknown means and changed himself into a girl to match her real life gender. She now sports long, unkempt, black hair and a long black dress. She makes a reappearance to intervene in a conflict between the Crescent Moon Refreshment Stand and the Landers.

Trivia

 * Magus makes a cameo along with Passhita and Coza in "The Skylarks Take Flight", walking with Dolce.