Heathcliff

A genius game developer and quantum physicist. The development director of SAO. Almost all the scientific technology related to the virtual world in this work is the result of his research and development. He was 30 years old at the time of the SAO incident. He came from the Shigemura Laboratory at Tōto Institute of Technology. From a young age, he had a fanatical desire to realize a "true otherworld," and while he showed his genius during his student days, he also revealed a dangerous side that would stop at nothing to achieve his goals. The phrase "This is not a game, even if it is a game," written in the work's introduction, originally came from an interview he gave to the media.

On the first day of SAO's official service, he declared the death game and monitored the game as a GM while hiding in a mountain lodge in Nagano Prefecture in the real world. At the same time, he disguised his appearance with an avatar and mingled with general players, forming the strongest guild in SAO, the Knights of the Blood Oath, and becoming its leader, "Holy Knight Heathcliff," leading the clearing group as a guide. When the clearing reached the 95th floor, he revealed his true identity and planned to face the players as the final boss on the 100th floor, but his identity was uncovered by Kirito right after the 75th floor was cleared. As a reward, he moved up the original schedule and fought a fierce battle with Kirito for the SAO clear, ultimately losing in a near-draw. When SAO was cleared, he attempted to leave his memory and personality as digital signals within the network by scanning his brain with high output, resulting in his physical death as his brain was burned out, but he succeeded in becoming digital.

He had secretly set up insurance to be able to log out and have GM privileges, making him systemically immortal, but he maintained a certain line in the clearing. After his identity was revealed, he disabled system protection and fought Kirito fairly. This attitude was later praised by Kirito as "never flinching in any situation," and although he committed an unforgivable crime, his will to pursue another reality had a significant impact on Kirito, making him think about the nature of the virtual and real worlds.

After the SAO incident, he wandered the cyber world in a dispersed data state but awakened by Kirito's cry while fighting Oberon to rescue Asuna in ALO. His thought-mimicking program granted Kirito the administrator privileges of ALO, leading to victory. After the battle, as a reward for helping Kirito, he entrusted him with "The Seed," a program to create virtual worlds, and disappeared into the cyber world again. Later, he reappeared on the "Ocean Turtle" during a crisis for Kirito and his friends fighting in UW, stopping a runaway reactor while under enemy attack, and returned to the cyber world once more.