.hack//AI buster 2 is a compilation of several stories that take place in different times in the .hack timeline.
.hack//2nd Character/Haruka Mizuhara's Situation
Haruka Mizuhara's Situation is the story of the first AI buster novel, except told from the point of view of Haruka Mizuhara and her alter ego Hokuto. It reveals details about Haruka's life and describes a turning point when she meets Albireo. The majority of the events in AI buster are told swiftly, although important conversations are retold word for word, this time with insight from Haruka. It is revealed that, through the course of her adventure with Albireo, she developed some feelings for him and wrote the Descendants of Fianna Poem to indirectly tell Albireo how she felt.
A sequel of sorts to the original AI buster novel, this story once again is told from Albireo's point of view. With the mystery of Lycoris still reverberating in his head, Albireo investigates Tsukasa and the illegal monster he is believed to control. He is confronted by Macha, who adds further doubts in his mind. After failing to strike Macha down, Albireo is attacked, his famous spear shattered, and the player Kazushi Watarai is knocked unconscious in the real world. Later, he meets Hokuto in real life as Haruka, and the two are implied to be living together.
Kamui focuses on Saki Shibayama, Albireo's former assistant and the new leader of the Cobalt Knight Brigade. Sworn to protect The World from hackers and cheaters she has launched a personal crusade against the data anomalies known as Vagrant AIs. She soon encounters a problem when she finds out that one of her subordinates Yukino has been in contact with an AI, and has in fact been protecting him from the Brigade. Kamui follows Yukino to a field, where she finds her playing with the AI, a young boy named Rin. Kamui reveals herself to the pair, announcing that she is here to delete Rin. Rin tries to convince Kamui that his life has as much value as hers, but she is unyielding. In her mind he is only a scrap of bugged data. Despite Yukino's protests Kamui deletes Rin, and leaves the field. Despite having performed her duty the experience haunts her, and she wonders if this was how Albireo felt after his encounter with Lycoris. Meanwhile, Yukino is quietly removed from the Cobalt Knights and placed into a clerical position instead.
Brigit, a Blademaster, begins to wonder why she plays The World after her partner, MAHO, decides to quit the game. She soon encounters a Vagrant AI named Rumor who tells her the legend of the .hackers. Intrigued, Brigit decides to continue playing The World, so that she can become a hero like the legendary .hackers. It is later revealed that Brigit was actually an old PC played by Rena Kunisaki, who would soon win a chibi version of the avatar of the .hacker BlackRose, and become a legend in her own right along with her brother Shugo.
Firefly follows Hotaru as she logs onto the JP servers for the first time. Though proficient in a little bit of Japanese she is quickly overwhelmed, and matters only get worse when she becomes the target of a user specific event. The event involves a fairy, visible only to her that asks her a strange riddle. "What is the one thing there are not two of in The World?" Confused, she asks for help only to be shunned by the Japanese players for speaking English. Luckily she runs into another American, a player named Sanjuro who volunteers to help her out. He takes her to a field, but the two become separated. Things get worse when Hotaru runs into a group of PKers, but Sanjuro arrives just in time to fight them off and save her. Sanjuro leads her to a lake swarming with fireflies, which causes Hotaru to figure out the answer to the riddle. It is her name Hotaru which means "firefly", written in Romanji. Hotaru thanks Sanjuro and prepares to leave, before she does so they exchange member addresses and he asks her to visit the JP server again.
- Macha (Cat)
- Brigit / Rena
- Rei Izumi's name is romanized as "Rei Idumi." Her name was originally spelled "Izumi" but was changed to "Idumi" at her request.
- Rumor was originally included in the Rena Special Pack, but was added here as well.
- In the chapter ".hack//Kamui" Kamui talks about the main System Administrator Ryos, however the main System Administrator's name is "Lios" this is due to a translation mistake.
- In "Firefly," Hotaru complains that the Boston Celtics have never come close to winning a national championship in almost 30 years. This runs under the assumption that the Celtics would not win between the time the story was written and 2014 when it occurs; however, the Celtics won the NBA Finals in 2008. It can be argued, however, that in the .hack universe, the Celtics never won the 2008 finals.
- AI buster 2 is the only numbered sequel in the .hack franchise.