Please Note : These arc titles are not official and do not appear in-story. These are compressed digest overviews of major events from the series. More detailed chapter entries are also available.
On the orders of Chief Kakuzawa, Shirakawa and Isobe go to bring about the release of Diclonius Silpelit Number 35, a girl named Mariko, the real daughter of the vanished Director Kurama, and likely the most powerful of her species. Kept under massive restraints and in virtual stasis, Mariko has bombs implanted in her body as a control mechanism, which becomes needed when she turns on and kills the scientist Saito, who naively saw herself having a parental bond with the girl. Her mission on the mainland is two-fold: kill Nana and re-capture but do not kill Lucy.
After some further rough patches with Kouta, Nana officially begins her new life at Maple House and enjoys it immensely, to the point she visits the beach to tell Bando that their deal regarding finding Lucy is off, as she does not wish to disrupt the happiness she has found. It is then she and Mariko, passing overhead in a chopper, sense one another. Since Bando is indifferent to any fight that doesn't involve Lucy, Nana quickly tells her new housemates to wait for her at home. She goes to directly confront Mariko when the chopper lands and is quickly overwhelmed by Mariko's far greater power. While Mariko pushes her controllers' patience by playing unmercifully with Nana, Kurama learns from the Chief of how Mariko has been sent to kill Nana, something Kurama refused to do. It also becomes apparent that the Chief's designs are far grander than anyone realized.
Nana's housemates await her return, the hope of which becomes far greater when Mariko's childish taunts finally push Nana into striking back, even disabling Mariko's vectors as she once did to Lucy. An angry exchange between the two girls about the worth of Nana's absent 'Papa' becomes moot when Kurama, father in a sense to both girls, arrives on the scene.