From Humble Beginnings

Six year old Akihiko Kayaba spends his days in the sandbox building sandcastle after sandcastle, trying to bring his dreams to life, most days leaving in disappointment. Until finally, one day, he creates something he's truly proud of, and his dream of Aincrad, the marvelous floating castle, is born. This is a one-shot of where Akihiko Kayaba got the idea for Sword Art Online.