The characters from previous .hack//G.U. Games and .hack//Roots receive an email from Ovan. He is requesting them to go to Hidden Forbidden Festival where is set up a mysterious summer festival. There they find an AIDA Chim Chim who wishes to peacefully co-exist with the other players of The World. It then transforms into the word "Returner", so they assume it to mean that Ovan will return to The World.

Subaru Sumeragi is the 13th head of the Sumeragi Clan and a most powerful onmyouji. Subaru is hired to exorcise a construction site, but his employer mysteriously died. The only suspect is a man who repeatedly walks away from situations in which he should have died. Then Subaru meets a young woman intent upon cursing the man, saying that he killed her brother. Subaru must figure out how his employer died and fight the evil spirits that are protecting the man with the help of his friend and twin sister, Seishirou Sakurazuka and Hokuto Sumeragi.

According to Kadokawa, an OVA of R-15 will be bundled with the tenth volume of the novel.

Tadashi Matsushita has recently entered the Kansai Fifth Technical High School and joined its notorious karate club. There he meets his captain, Yoshiyuki Takagi, an incredibly strong individual. Feared and respected throughout Osaka, Takagi is deep down an honorable and compassionate guy despite his violent endeavors.