曾几何时，世界上突然出现无数身形庞大的巨人，普通人类的生命受到前所未有的威胁。为了保护自身安全，最后的人类筑起三座高墙：玛莉亚、露丝和希娜。人类迎来了长达一个世纪的和平岁月，却也让自己成为圈养在笼中的鸟儿，屈辱地失去自由。845年，高达60米的超大型巨人和铠之巨人登场， 摧毁了最外层的玛莉亚之壁，也惊醒了人类似乎永远不会苏醒的长梦。在此事件中，不愿蜷缩在墙内的少年艾伦·耶格尔（梶裕贵 配音）亲眼目睹母亲遇害，由此更坚定了他加入调查兵团的决心。在此之后，艾伦和青梅竹马三笠·阿克曼（石川由依 配音）、好友阿尔敏·亚鲁雷特（井上麻里奈 配音）加入第104期训练兵团，发誓成为足以消灭所有巨人的英勇战士。百年的和平结束，人类和巨人的战争再度拉开序幕……
本片根据谏山创的同名原作改编。

Yuta Togashi has a problem. He used to be a "chunibyo," one of the thousands of Japanese students so desperate to stand out that they've literally convinced themselves that they have secret knowledge and hidden powers. But now that he's starting high school, he's determined to put aside his delusions and face life head on. The trouble is Rikka Takanashi, his upstairs neighbor, is just a little bit delusional herself. And she knows all about his past indiscretions.

宿海仁太（入野自由 配音）、本间芽衣子（茅野爱衣 配音）、安城鸣子（户松遥 配音） 久川铁道（近藤孝行 配音）、松雪集（樱井孝宏 配音）、鹤见知利子（早见沙织 配音）6个人曾是童年最要好的玩伴，他们彼此亲密无间，以各自的绰号相称。6个小家伙甚至建立了一个秘密基地，并给他们这个小团体命名为“超平和Busters”。然而，一场意外让孩子们的心中互生芥蒂，随着年龄的增长，他们渐行渐远，走上不同的人生旅途，彼此失掉了联系。某天，“面码”芽衣子突然出现在仁太的面前，仁太惊讶的发现芽衣子的容貌和性格几乎从未被时光所改变。在芽衣子的号召下，失落的好友们重新走到了一起……
本片为A-1 Pictures的原创动画，共11话。

In the year 2022, a massive online role-playing game called Sword Art Online (SAO) is launched. With the aid of "NerveGear" technology, players can control their avatars within the game using nothing but their own thoughts.

Kazuto Kirigaya is among the lucky few who get their hands on the first shipment. He logs in to find himself, with ten-thousand others, in the scenic and elaborate world of Aincrad. However, in a cruel turn of events, the players soon realize they cannot log out; the game's creator has trapped them in his new world until they complete all one hundred levels of the game.

In order to escape Aincrad, Kirito will now have to interact and cooperate with his fellow players. Some are allies, while others are foes. Sword Art Online is not all fun and games: if they die in Aincrad, they die in real life. Kirito must adapt to his new reality, fight for his survival, and hopefully break free from his virtual hell.