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In the year 2022, the gaming industry has reached a new height after the development of the NerveGear, a helmet-like controller that allows the user to fully dive their senses into the world of virtual reality. After a closed beta with only 1,000 testers, the Virtual Reality MMORPG Sword Art Online is launched. The game takes place within a floating castle of steel called Aincrad where thousands of monsters are found in its 100 floors, and the players are given an array of medieval inspired weapons to use.

Yukiteru "Yuki" Amano is a loner who spends most of his time writing a diary on his cell phone or talking with his imaginary friends Deus Ex Machina, the God of Time and Space; and Murmur, Deus' servant. One day, Deus gives Yuki a special diary, mentioning something about a game. Strangely, Yuki's new diary has entries in it spanning the next 90 days—entries about the future that come unnervingly true. Deus, the not-so-imaginary God of Time and Space, then forces Yuki to participate in a battle royale with eleven other people, each of whom also has a diary that can predict the future in some unique way. The rules of this "Diary Game" are simple: the contestants must try to find and kill all the other contestants before the world ends on Day 90, and only the last one standing can prevent the Apocalypse and become the new God of Time and Space.

The suspense horror/dark fantasy story is set in Tokyo, which is haunted by mysterious "ghouls" who are devouring humans. People are gripped by the fear of these ghouls whose identities are masked in mystery. An ordinary college student named Kaneki encounters Rize, a girl who is an avid reader like him, at the café he frequents. Little does he realize that his fate will change overnight when he follows her along and eventually gets turned into a ghoul himself.

The story follows Rico, an orphan who dreams of becoming a great cave raider, much like her mother, and solve the mystery of the Abyss. The Abyss is an unexplored enormous cave system inhabited by strange and wonderful creatures, along with mysterious artifacts. Generations of bold adventurers have been drawn by the cryptic depths of the Abyss, and over time came to be known as "Cave Raiders." One day exploring the murky depths she stumbles upon a little boy, who turns out to be a robot.

Sora and Shiro are a pair of siblings, brother and sister, who are well known as brilliant. Yet they are NEETs - useless to society, and (Not in Education, Employment, or Training) - and even worse they are completely house-locked shut-ins (hikikomori!). Their reputation as gamers has spawned urban legends all over the Internet. These two gamers even consider the real world as just another "crappy game." One day, they are summoned by a boy named "God" to an alternate world. There, God has prohibited war and declared this to be a world where "everything is decided by games"—even national borders. Humanity has been driven back into one remaining city by the other races. Will Sora and Shiro, the good-for-nothing brother and sister, become the "Saviors of Humanity" on this alternate world? "Well, let's start playing."