In the online RPG "Union" was Subaru, a party of grade school players. One day, two of its members Asahi and Haruto exchanged a promise and a ring. But Asahi sacrificed herself to protect Haruto and also died in real life. The game then suspended operations and the members of Subaru went their separate ways. Six years later, Haruto logs into the newly released "Re'Union" and reunites with Asahi.

Haruto is shocked by Asahi's sudden appearance in Re'Union six years after her death. Asahi acts as if nothing has happened, although she's unable to log out from the game. Players have noticed Asahi's existence and try to take her, but the former Subaru member Takanori appears. He had become the leader of the elite guild Illuminati. Asahi suggests reassembling Subaru, but...

Having reunited with Asahi in Re'Union, Satsuki asks Asahi to stay away from Haruto for his sake. However, Satsuki realizes that she was jealous of Asahi after witnessing her share a moment with Haruto six years ago, and vows to herself that she won't lose this time. In order to find out Asahi's identity, the three of them head to the dungeon where Asahi got her game over all those years ago.

The three Subaru members defeat the boss Purgatorio responsible for Asahi's game over. Upon his defeat, they see mysterious images inside their heads, and Asahi suspects they are her memories. They set out to find the remaining Subaru members when they are surrounded by members of the elite Southern Cross guild who are after Asahi. They're soon joined by a different guild called the Brill Society.

The elite guilds Southern Cross and the Brill Society capture Asahi after Takanori falls for their ruse. In order to save Asahi, Haruto goes up against thousands of enemies alone, but ends up outnumbered until Satsuki and Takanori come to his aid. The three of them finally reach Asahi, only to discover that Angelus has taken control of her spirit in order to control the Prophet Art.

Haruto wakes up to the sound of a beeping EKG to find Asahi standing over him. "I'd be surprised if I were you, too. You've been asleep for six years," says Asahi, who came with Satsuki and Takanori to visit him. Asahi explains that Haruto got a game over when he protected Nozomi from Purgatorio. However, Haruto isn't satisfied with the explanation and questions them about Re'Union.

In Re'Union, Haruto retakes possession of Pleiades, which holds the power of the members of Subaru. Clive received a request for help from Elicia, and tells everyone that Elicia says that in order to stop Gnosis from awakening Asahi, it is necessary to awaken all the members of Subaru. Meanwhile, Haruto and Satsuki reunite with Nozomi in the real world, and ask her to log into Re'Union again.

After getting rejected by Haruto, Satsuki tries to sort out her feelings and reminds herself they're still childhood friends. Meanwhile, Takanori tells them that Nozomi has gone missing in real life. With Clive's help, they find out that Nozomi is logged in to Re'Union and go to find her.