Background
Kazuto Kirigaya
Better known through his gamer tag "Kirito," he is the main protagonist of Sword Art Online. Through his intelligence and fascination with computers, Kirito was the first of a thousand testers to try out the first Virtual Reality MMORPG: Sword Art Online.
However, when he got the full game, fun became the least of his concerns as the creator revealed to the ten thousand players that they got trapped in the game. And that if they died in the game, they'd die in real life. Using his intellect and knowledge of the game, Kirito quickly rose through the ranks, eventually becoming the hero of Aincrad and finishing the game for everyone.
Personality/Tactics
Due to his loner personality and superior gaming skills, Kirito is not the most social person, often teasing others unintentionally or having an air of overconfidence. Either way, Kirito is often calm, cool, and collected, rarely ever getting too emotional, usually being able to think rationally even in dangerous situations. After the deaths of his first guild, Kirito's antisocialism and stoicism became all the more rampant, a trauma that often pushes him to help anyone in his way—portraying a kindness underneath his stammering.
Tactically Kirito is a highly adaptable opponent, often being able to predict and take charge in fights. After unlocking the dual wield ability and facing stronger opponents, Kirito started to gain a larger focus on offense, using his superior speed and strength to overwhelm his opponents up close. He's willing to take massive grave injuries even in the midst of his offense if it means taking the win.
Powers/Abilities
As both a player and beta tester of Sword Art Online, Kirito gained a variety of gear throughout his two years. Overall though, as one of the highest leveled players, Kirto establishes superhuman strength, speed, agility, stamina, and durability. As his level grew, Kirito displayed multiple high-level detection skills to help track people. Being a player, Kirito also accesses a massive inventory and heads up display for his allies and opponents' help.
In terms of sheer ability, Kirito's experience in SAO made him a highly effective but unorthodox combatant and swordsman. He is also immensely gifted in terms of intellect, able to easily remember and pick up on his opponents' small details. Kirito also has a natural interest in computers and mathematics, leading him to be a skilled programmer and hacker.
Techniques
Starburst Stream: A devastating 16-hit Sword Skill wielded with two swords.
Equipment
By the end of Aincrad, Kirito featured his iconic Blackwyrm cloak, numerous healing potions, and teleporting crystals (can't be used in battle, though). Most importantly, though, Kirito uses two swords, the Elucidator and later the Dark Repulser, in tandem with one another.
Feats
Due to using the Dual Blade ability Kirito has the fastest reaction speed in SAO.
With the help of Dual Blade ability, Kirito was capable of defeating the 74th-floor boss, the Gleam Eyes, nearly by himself.
Kirito was capable of beating Heathcliff, who initially served as SAO's strongest player and secret 100th boss, in a one-on-one.
Tanjiro Kamado
Background
Tanjiro Kamado is the main protagonist of Demon Slayer. Initially, he was just an ordinary boy living with his large family in the mountains. However, on a snowy night, Tanjrio returned home to see his family slaughtered with his sister Nezuko turning into a demon. With his life forever changed, Tanjiro decides to become a Demon Slayer, warriors tasked with slaying the nocturnal creatures. All so he could cure his sister and find his family's killer.
Personality/Tactics
Tanjiro is all around a kind and honest yet naive soul. He is willing to help anyone in need and takes their word at face value. His determination is also unparalleled as he tirelessly will train and work if it means achieving his goals. His ability to empathize with others is so strong that Tanjiro feels sorry for the demons he slays and wishes to give them peaceful deaths. However, there is a limit to his kindness. When he gets pushed too far, Tanjiro's rage is terrifying. This displays a far more strict and cruel side towards enemies. However, this same rage can lead him to become a little reckless.
Due to the demon's regenerative powers, Tanjiro often uses his nose to track their most significant weak point: the head. Combined with the water-breathing swordsmanship style, Tanjiro is a highly maneuverable defensive fighter who quickly closes the distance. The style's innate flexibility combined with Tanjiro's mind usually gives him the tools to brave through his opponent's techniques till he figures them out.
After unlocking the higher power and more draining, Hinokami Kagura Tanjiro started to regularly phase those techniques in and out to disrupt and deal out more damage either by switching or combining breathing styles. Tanjiro will also use his hardhead to stun opponents as a last resort.
Power/Abilities
Like most Demon Slayers, Tanjiro is proficient in using the Breathing styles, martial arts designed to increase the flow of oxygen in the body to increase all physical and mental performance a hundredfold. Advanced users like Tanjiro can even permanently and unconsciously do this. In his fight with the Upper Moon Demon Gyutaro, Tanjiro also accessed (albeit briefly) the demon slayer mark, which increases a Slayer's power even more.
Before learning this, he already had a tough head, impeccable sense of smell, and will that could make him brave through immense pain and injuries.
Tanjiro is a natural-born fighter. His keen mind can quickly deduce the mystical powers of his demonic opponents and make appropriate countermeasures. This also goes towards training. He has notable skill in unarmed combat.
As a practitioner of two breathing styles, Tanjiro is near unparalleled in swordsmanship, with an accuracy to match. With the power of Water Breathing, Tanjiro can mimic the elements' winding, fast footwork, and dynamic movements to maneuver at almost any angle while picking up speed smoothly. Sun Breathing is far more powerful though capable of dramatic swings and faster movements to disrupt the opponent.
Equipment
Tanjiro carries a Nichrin Blade, a weapon made from a specific metal that counterattacks.
Feats
Despite being a novice, Tanjiro, through his Sun Breathing alone, was capable of overpowering the Upper Moon Six Demon Daki by himself. A feat that not even Hashira, the top fighters in the Demon Slayer Corps, could do.
With help from his fellow demon slayer, Insouke Tanjiro was capable of slaying Enmu, the top of the lower Moon level Demons. A feat that nearly puts him on the level of Hashira.
To overcome the weaknesses of both Water and Sun breathing, respectively, Tanjiro on the fly was shown to combine both styles, something never before seen by any Demon Slayer.
Location
SAO: 74th floor Boss Room