Arachus is a monstorous creation of The Agency. Arachus used to be Dr. Van Miller, who worked for The Agency on several projects. However, she soon began to feel guilt about turning innocent people into zombies and decided to go public of The Agency's actions. But she was caught and imprisoned. Mr. Black decided that Miller would become the subject of the newest experiment and Miller was experimented on for months.
Miller was first injected with the T-Virus and transformed into a zombie. After that, both her arms were cut off and replaced with huge spider-like mechanical limbs. Several more giant mechanical legs were added to her and Miller became a creature codenamed Arachus, due to her resemblance to a spider. Arachus was hostile toward all personal and had to be locked away. Mr. Black planned to outfit Arachus with a control harness to make the creature more obidient, but before he could, S.T.A.R.S. members attacked Island One.
After the power was knocked out, Arachus broke free of its containment cell and stalked the island, killing several Rippers, zombies, and security guards along its path. Mr. Black calculated it was hunting him, saying that Miller's conciousness was somehow still alive in there and it remembered what Mr. Black had done.
As Island One began its self-destruct countdown, Alan, one of the last surviving members of the team, made his way to the helipad to be evacuated. However, he was confronted by Mr. Black and the two shared a tense exchange. Mr. Black prepared to shoot Alan, but suddenly, Arachus burst through the floor. Mr. Black immediatly made a run for it, succeeding in escaping in his helicopter. Arachus then turned its attention to Alan and Alan was forced to fight the creature. He succeeded in killing it, and Arachus fell off the helipad port to its death one hundred feet below.
Arachus is the final boss of Resident Evil: Island One. It is a very tough boss, and will constantly chase Alan around the small helipad port. It will attempt to crush him with its giant legs, and also swing its giant arms. Each of these attacks in a instant kill. Its only weak point is its body, and it constantly shields that with its legs. To kill it, Alan much destroy each of its legs with a heavy weapon, swung as a grenade launcher or a rocket launcher. After a leg is destroyed, Arachus will temporarily fall to the ground, leaving it open to attack. Flamethrowers and shotguns are extremely effective at damaging its main body, but it will attempt to get the player away by flailing its arms wildly. After a minute, it will get back up and resume chasing Alan. When it is damaged enough, it will stumbled backwards toward the edge of the helipad, but grab onto Alan's leg, attempting to drag him over the side. Alan must shoot it several times before it falls over and it will let go, and fall to its death.
Arachus is the final boss of Resident Evil: Island One.