In a Massively Multiplayer Online Role-Playing Game called the World, everything is just fun and games. However that is not the case with Tsukasa. He is unable to log out of the World and, unlike other players, he can feel pain. However, he also gains a Guardian with immense power. Mimiru befriends Tsukasa and is shocked to discover his condition. She and Bear try to help but Tsukasa ends up attracting the attention of the Silver Knights, the moderators of the World. After Tsukasa's Guardian struck down their second-in-command, Silver Knight, and several other players, Subaru, the leader of the Silver Knights, though hesitant at first, calls for the capture of Tsukasa. However, as they go deeper into the mystery surrounding Tsukasa's problem, things become more complicated as the problem sprouts from the very core of the World.
Haseo starts playing and experiences PKers (Player Killers). After they kill him, Ovan revives him. Then almost all the players in the world start asking him about Ovan.
Haseo shows obsessive behavior toward Ovan's mysterious guild. He asks around to find more about it. At the end of the episode, he meets Ovan by a portal. Ovan asks Haseo to join his clan. Haseo responds by saying, "I'll think about it."
Haseo is given an invitation to join the Twilight Brigade as well as one to join TaN. After expending a little time with Shino, Haseo makes his decision.
Shino takes Haseo to another Lost Ground, and later do training. SakiSaka gets suspicious about why Haseo joined and why he talked to Gord about the guild. Later Tabby gets pked by Ender.
During a meteor shower, SakiSaka's loyalty is put into question, as Ender attacks he and Tabby. The game experiences glitches, and Haseo displays a new ability when he arrives to help the two.
Due to a series of events, Tabby starts believing Haseo is a messenger for TaN and soon later Haseo leaves the Twilight Brigade. Haseo is then seen by Tabby and Shino talking to a TaN member who called him. .
While investigating the Lost Grounds, Haseo experiences a major glitch in The World. Also, we learn more about the Virus Cores. On a team search with Tabby and SakiSaka, they find common marks in the Lost Grounds, where they had found virus cores. Haseo notices something weird about the lines, and the three mysteriouly vanish (presumably teleported).
Haseo, Tabby, and SakiSaka find out the lines they found are portals. Continuing their search of the Lost Grounds, Tabby and SakiSaka encounter a glitch, while Haseo is confronted by Ender. Haseo notices the multiple colors of the Virus Cores, in comparison to the pillars from one of the Lost Grounds. This news comes as a breakthrough to the Key of the Twilight, as Haseo finds another Virus Core.
The Twilight Brigade attempts to bring together all of the Virus Cores. SakiSaka is given the last Core by Tawalaya, while Gord and B Set show up to help the Twilight Brigade, who are being attacked by TaN. They are then transported to an unknown location, while Ender and her TaN subordinates follow. (Known as "Melee" inside North America.)
The Twilight Brigade holds against TaN while Ovan goes to find the Twilight Key. Passing through a door, he steps into a trap (later we find out, knowingly) set by Naobi and the rest of the TaN. Later, Shino threatens TaN with revealing certain illegal activities online, if Ovan wasn't returned. TaN disbands, and Ovan is left captive, his PC data being read by Naobi.
Gord is thinking of quitting the game. Several TaN members are getting banned because of their illegal activities that Shino handed in to the administrators.
The guild called the Twilight Brigade is being disbanded by Shino. Gord and B-Set quit the game because Ovan is no longer there. Haseo promises to stay with Shino even if there was no guild. Shino decides to wait for Ovan to return.
Tabby notifies Haseo that Shino has entered the Cathedral alone. When Haseo goes to meet her, he finds that Shino has been PK'd and her character data disappears.
Haseo gets upset about Shino and blames himself. He gets a call from Shino's mother and cannot tell her anything about her daughter's coma. Phyllo is with Haseo most of the time and Tabby starts a guild with Sakisaka but he resigns his guild and leaves to a new game, which made Tabby all by herself in the game making her lost without anyone but Haseo.
Tabby meets two new members of the The World. She helps them play the game but says she can't do better like Shino and Sakisaka. Tabby meets Kuhn with Phyllo and Kuhn trains the two newbie brothers and Tabby about the game and how to level up in the game. Haseo is still angry about what happened and remembers the deletion of character data of Shino's and wants revenge on Tri-Edge.
Ovan meets Taihaku and while that happens Taihaku goes to the Forest of Pain. Haseo hears about Phyllo encountering Tri-Edge and talks to Phyllo and he tells Haseo don't blame himself for her coma. Haseo fights and loses to Phyllo who tells him not to fight Tri-Edge because he will most likely become "Unreturned." Haseo then hears about the new quest and takes it to become stronger and defeat Tri-Edge.
Saburo befriends Tabby, who still worries about Haseo. Yata and Pi try to figure out Phyllo’s relationship with Ovan because he is the only survivor of Tri-Edge. Taihaku and Haseo are in the Forest of Pain. Pi tells Subaro to make contact with Haseo in the forest and see what he does in there. Ovan fights Tri-Edge. Taihaku completes the quest and Tabby decides to go to wait for Haseo.
Taihaku gets his reward a new and rare Steam Gunner weapon. Tabby waits with her friend for Haseo to exit the quest. Haseo made it to the end where he sees a man and he request Haseo to answer his question, Haseo says something negative about his daughter and exited the quest about 30 seconds before the game ended. Haseo appears to Tabby but this time Haseo is different than usual; the shock somehow boosted Haseo to his 3rd adept rouge class, Flick Reaper.
Tawaraya returns as Tohta to finish up some business and finds out that merchants that buy rare items with real money and have driven up the prices. He sets out to stop them while Yata continues to watch Haseo.
Haseo goes half-crazed, searching for information on Tri-Edge by hunting and pking PCs. Saburo fights Haseo, trying to bring out the factor that Yata and Pi are interested in but fails. Taihaku talks to Phyllo about the Forest of Pain and Haseo. Tohta makes contact with Haseo and earns his trust.
Haseo fights Midori who easily dodges his attacks. Haseo wants information from her because she is a survivor and witness of Tri-Edge. He continues to pk PCs, frustrated that he cannot meet Tri-Edge. Meanwhile, Tabby and Seisaku start a guild to help Haseo and the PCs that he pks.
Tabby and her guild fail at their debut to heal people; Tohta makes them to level up. Kuhn awakens his power and is scouted by Pi to join her guild. The Paw Squad start to heal Haseo’s victims and he does not stop them.
Haseo starts to pk the PKers hoping to come across Tri-Edge who is a PKer. All the PKers band together to fight Haseo. Kuhn is introduced to Yata’s guild, Raven. The Paw Squad goes to heal but Haseo kills everyone and all but Tabby leave the guild because they don’t want to help Haseo anymore.
Haseo is now “The Terror of Death” and refuses to listen to anyone or accept help. Tabby is lost as to what to do. Haseo meets Ovan and is sent to the Cathedral where he fights Tri-Edge.
Seisaku talks to Tabby who decides to stop relying on Haseo. Ovan tells Phyllo something shocking. Phyllo entrusts to Tohta a heavy burden. Tabby and Saburo talk about Haseo and life.
Haseo has emerged from inactivity after his defeat at the hands of Tri-Edge. He encounters Tohta and learns about Phyllo, missing him. Tabby meets with Haseo to let him know of her real life ambitions. Once Haseo is left alone, the episode recaps the events during the series between Shino and Haseo, leading into a scene in which Haseo sees a "ghost" of Shino. The episode ends with a brief glimpse of Haseo in his Xth Form from the G.U. games, with the avatar Skeith in the background. The image transitions back to the present Haseo, and Haseo looks into the distance, with renewed determination to continue his search.