Kagemamoru was the main villain of Season 1. It was a virus created to protect TOME that went rogue. In TOME, it is presented as being more enigmatic and mysterious, with background information calling it Kajet.
Kagemamoru was originally designed and envisioned as a virus-like guardian for TOME by an unnamed 3rd party developer (later revealed to be Darkeyesofanubis). It was supposed to act as an automated GM: punishing those who broke the rules, and so on. Unfortunately when Kagemamoru was released into TOME it began to go on a rampage. Fearing damage to Motherboard, theNetkings attempted to battle it, but failed, and it was only through both hacking and editing the virtual space around it that allowed the virus to be initially stopped. During the fight, Kagemamoru demonstrated an ability to affect users in the real world. Most of the Netkings sustained minor injuries in real life from the fight, but Zetto, who lost his arm during the battle, suffered the most.
Years later, Kagemamoru was unintentionally freed by Alpha when he managed to find his way into its prison by a glitch. It struck a deal with Alpha, offering him power in exchange for "help." Not knowing any better, Alpha agreed and Kagemamoru attached itself to him. This merger allowed Alpha to go into a "berzerker mode," and allowed Kagemamoru to regain its strength.During a fight in episode 22, Kagemamoru gets drained from Alpha into Zetto's arm, but Kirbopher15 drains Kagemamoru from Zetto into a Drain Sword and then breaks it.
Having regain its strength and no longer merged with any players, Kagemamoru proceeds to continue its rampage. Kagemamoru is defeated by a joint attack by Alpha and Kirbopher, which shatters it into hundreds of pieces.
These peices return in Season 2 as the D-Bug Organization's target, called "Virusfrags".