Akihiko Kayaba

Akihiko Kayaba is the development director and Game Master of Sword Art Online. He is also the designer of the NerveGear, the Cardinal System and The Seed, as well as the main antagonist of the Aincrad Arc. He plays SAO as the leader of the Knights of the Blood, Heathcliff.

Appearance
Akihiko Kayaba is the only player in Sword Art Online whose avatar does not match his appearance in the real world. As a result, Kayaba's avatar, Heathcliff, bears no resemblance to his true skinny body.

Significantly idealized, Heathcliff is muscular, tall, and physically strong. With a cool demeanor, he is almost always seen wearing the colors of the Knights of the Blood.

At the start of Sword Art Online, Kayaba appears to the trapped players as a faceless, hooded person with a cloak as his Game Master avatar.

Personality
Although Akihiko Kayaba only appears as his true form few times throughout the series, he is always very calm, soft-spoken, and has a cool demeanor. Despite being incredibly skilled, Kayaba is not boastful and when Kirito does defeat him and clears Sword Art Online, he humbly accepts his defeat.

He seems to be very sincere and thoughtful in everything he does, as shown when he tells Kirito of his dream about creating a floating castle, as the basis for creating Sword Art Online in the first place.

Kayaba Akihiko has little to no empathy, no regard for human life including his own. Instead he is completely taken in by the virtual world. When he accidentally struck Asuna, which caused her apparent in-game death, he showed no remorse, and instead seemed rather amused, even though it caused Kirito an incredible amount of grief at the time. He chose to fulfill his dream by making a Death Game which cost thousands of lives, and simply noted that their minds were gone from both worlds forever. All this was simply to make his virtual world more "real" in his eyes. His fascination with computers is just very much like Kirito's, with the major difference being Akihiko having no regard for the lives of others, and Kirito doing everything he can to protect them. His goal was to make a world that was not bound to physicall limitations.

In spite of this, Akihiko has a level of honor, and fairness even noted by Kirito. He designed Sword Art Online to be a beatable game, by anyone who had the skills to do so. He never interfered with the players' progress to keep them from advancing through the game; in fact, as Heathcliff, he was actually fighting on the players' side, helping them clear floors. The one exception to this is the fact that he made himself invincible until his battle with Kirito, although this was necessary to survive the game until the 95th floor was reached since until then it was to help the players. Heathcliff planned to reveal his true identity and become the final boss on the 100th floor to test the remaining players skills.

History
In Kayaba's childhood, Kayaba expressed an interest in reading books. He was not particularly engrossed in games in computers, but he participated in the Mathematics Club of his high school. Later on, in university, he did not participate in any circles because he frequently worked in and out of laboratories.

When he began developing Sword Art Online, Kayaba toiled for years to develop the game software. In the anime, his main goal and dream was to "make Aincrad float" but after he did so, he wasn't entirely sure what his dreams, aspirations, or purpose were. In the original light novel, however, he explains more thoroughly that he felt frustrated and limited by the arbitrary rules that govern the current reality and wished to exceed them by supplanting it with his own. This desire went to the extent that he is actually happy to see Kirito and Asuna surpass the established laws of the virtual world he created.

It can be deduced that Kayaba began working on Sword Art Online before his third year in university. His love interest was Koujiro Rinko, who assisted Kayaba for ten years of the game's development, and took care of his body during the course of Sword Art Online.

His avatar, Heathcliff is the leader of what is considered to be the Sword Art Online's strongest guild Knights of the Blood. He is the owner of the first Unique Skill Holy Sword and is considered to be strongest player in-game. He wields the one-handed sword and a tower shield collectively called as Liberator. He also was able to hold off the boss of the fiftieth level for ten minutes by himself, which earned him the title Man of Legend. It is also rumored in Sword Art Online that Heathcliff's health has never gone into the yellow zone. This is due to his identity being Kayaba Akihiko and being able to make himself invincible or otherwise making his character into an Immortal Object after his health reaches 50%.

As a leader of the Knight of the Blood, Heathcliff was quite renown for his general tendency to stay out of guild affairs, preferring to allow his sub-leaders to develop plans and advance the game. Apart from guild paperwork and battles, Heathcliff rarely interfered with the choices and actions of his sub-leaders. The only exception to this was when Asuna expressed her wish to leave the guild, and Heathcliff refused to allow her do so without challenging Kirito to a duel.

Kirito first suspected his true identity during his match against Heathcliff when Kirito saw that Heathcliff's speed exceeded the system limits. However, Kirito figures out his true identity in the 75th floor. Thanks to a miracle in the game allowing Kirito to launch one final attack after his HP ran out, Kirito manages to defeat Heathcliff and free the trapped players from the cursed death game.

Even before the SAO incident occurred, Kayaba had decided to die along with  the game, though his choice of death was rather unusual. After SAO was cleared, he used a remodeled FullDive machine (the design of which was later used in the creation of the MediCuboid, which in turn was used to create the Soul Translator) to perform a super-highpowered scan of his brain to transfer his consciousness into the virtual world permanently. This scan led to burning out his brain cells ultimately killing his body.

Although the scan only had less than a 1 in 1000 chance of succeeding, apparently the scan was successful, as he makes a reappearance in ALfheim Online. He notes that his program was only recently awakened after hearing Kirito's voice during his encounter with Oberon. When Kayaba sees Kirito giving up and submitting to the power of the system, he reminds the swordsman about their battle, where Kayaba was forced to acknowledge the power of the human will over machine, and encourages Kirito to stand and take hold of his sword. After Kirito stands up and grabs the fist of Oberon, who attempted to punch him, Kayaba reveals his administrator ID and password to Kirito, allowing him to access Heathcliff's account. In terms of administrative power it over-ranked Oberon and allowed Kirito to easily defeat Oberon. After Oberon is destroyed and Asuna is logged out, Kayaba returns and entrusts Kirito with the World Seed, as a compensation for helping Kirito. Although Kayaba wishes to have the seed sprout, he leaves the choice of what to do with it to Kirito as he disappeared into thin air.

Following the web novels at the end of the Alicization arc Kayaba sacrifices his existence in both the virtual world and physical world by transferring his full consciousness into a robot body in an attempt to save those on the Ocean Turtle when its reactor starts to have a meltdown. Kirito and Yui confirm he's dead after this and apparently stops the meltdown at the cost of the robot and his own life.

Abilities
His abilities are Holy Sword, One-Handed Straight Sword, Hand-to-Hand Combat, Heavy Metal Equipment, Battle Healing, Searching, Tracking, Spiritual Light and Immortality.

Trivia

 * Aside from research and development, Kayaba's hobbies are cooking and Go (the board game).
 * The first RPG Kayaba played was an old RPG known as Wizardry. It apparently played an influence on the development of Sword Art Online.
 * Kayaba intended to reveal his true identity on Sword Art Online on the 95th floor, and become the final boss on the 100th floor.
 * Kayaba admits that he wouldn't be able to win against the youth with his actual reflexes.
 * Kayaba had spared no attention to the existence of Yui and later admits that he regrets it, saying that it was a great opportunity that has gone by.
 * The happiest moment to Kayaba during SAO was when Kirito saw through his true identity on the 75th floor, as Kayaba then realized that he (Kayaba) was nothing more than another player.