Having been captured by Kyôka, Minerva, held in Hell's Core of Tartaros, finally leaves her flask, reborn as a Demon and is welcomed by Jackal and Tempester as a new part of the guild. Meanwhile, after Seilah's plan to massacre Fairy Tail fails and the Mages invade Cube, Kyôka hastens to reach the place where Erza is in order to use her as a hostage, however, as she arrives, she is instead caught by Natsu and Lisanna. After tying the Demon up, the two leave to look for Mirajane while Erza questions Kyôka for Tartaros' plans. It's not long before Kyôka frees herself and the fight between the Demon and the Mage ensues. Eventually, Erza makes use of a giant lance to strike Kyôka and break through the Cube, making an entrance for the rest of Fairy Tail.
However, Kyôka is not done for and drags Erza away from her guild mates to continue their fight. It doesn't last for long as Kyôka soon realizes that the Face plan has failed and decides to leave, with Minerva taking her place instead. Erza is both surprised and disgusted to see Minerva's new appearance as the newly-reborn Demon states that she is now to be called "Neo Minerva".
- The details of the beginning of this battle are unknown.
Some time later, Erza is seen clashing with Minerva just as Warren Rocko contacts the Fairy Tail Mages through his Telepathy. Erza then yells out Warren's name as she notices Mard Geer hijacking into Telepathy. Surprised, she listens to Mard's words, followed by the activation of Alegria, which causes her to be sucked into the walls of Cube. Not wanting to let her go, Minerva charges at Erza, receiving an angered expression from the latter, but Minerva's efforts are futile as Erza completely falls prey to Alegria, much to the Demon's anger, and later, sadness.
However, thanks to Lucy Heartfilia's actions, the Celestial Spirit King casts Galaxia Blade in order to get rid of Alegria and Minerva, surprised to see the light, is suddenly attacked by now-revived Erza. Excited, Minerva welcomes this new development and tells Erza to show what she's made of, just as the two clash.
The two continue exchanging blows, with Erza attempting to talk to Minerva, but the Demon corrects her, saying that she's now "Neo Minerva" and exclaims that she's been reborn as the ultimate Mage, breaking Erza's sword into two. While in mid-air, Erza readies to deliver a kick, but Minerva makes use of her Territory to switch places with Erza and strikes her instead. With a smirk on her face, Minerva tells Erza to have more fun together, but before she can finish, Erza is already next to her and, with great power and speed, hits Minerva's face. An angered Minerva attempts to retaliate against this, claiming one more time that she's the ultimate Mage, but Erza questions her reason for fighting and delivers another destructive punch.
Recalling her past and her father's punishment for being weak, Minerva gets up to strike Erza in order to prove her strength, but Erza yells at her to wake up while punching her into her face one more time. Erza then comments on Minerva's actions during Grand Magic Games, claiming that she understands they were for Sabertooth's sake. Minerva is silent until Erza states that her fist is crying for being involved in such meaningless fight, which is when Minerva smiles and asks Erza to use that fist to kill her. She continues by claiming that she's weak and thus she succumbed to the darkness. However, Erza argues that there is surely someone waiting for Minerva to come home, so she shouldn't ever forget that and Minerva looks at Erza, with an expression full of hope.
That is when the two are approached by Mard Geer. The Demon comments on the conversation he has just heard and belittles humans for always rambling on about life and death. Erza realizes that this voice belongs to the Underworld King, while he continues his speech, disappointed that because of the Celestial Spirit King's actions, he has to go into battle himself. Smirking that he can devote a bit of his free time to clean up the place and after Erza asks whether he is the master of Tartaros, Mard blows the two away with a simple movement of his arm and then proceeds aiming his next attack for Minerva. While Erza is shocked, Minerva smiles, telling the Fairy Tail Mage to run away. An explosion ensues, however, Erza soon witnesses Sting Eucliffe, carrying Minerva, who arrives along with Rogue Cheney, Lector and Frosch to aid their lady.