Lucy Heartfilia vs. Tartaros is a fight fought between Fairy Tail Mage Lucy Heartfilia, and several Demons of Tartaros: the Underworld King, Mard Geer Tartaros; Nine Demon Gates' Torafuzar and Jackal; Lamy and Tartaros' henchmen.
Franmalth falls after Natsu's attack and Lucy, relieved, watches as all the souls stolen by the Demon are returning to their appropriate places. Suddenly, the soul of Hades appears behind the Mages, warning them of Tartaros' true plans and tells them to let Makarov know to "let the light out." The group is taken aback and Happy soon decides to leave in order to reach Master. Lucy, while worried about Gray fighting against his opponent, decides to continue their search for Mirajane, when suddenly, they are contacted by Warren Rocko through his Telepathy. It is revealed that Mirajane is safe and Lucy lets everyone know that Wendy and Carla have stopped Face.
Not long after Happy relays Hades' message to Makarov, their Telepathy is hijacked by Mard Geer, who, after introducing himself, tells the Fairy Tail Mages that they have no future and activates Alegria. Cube shakes and its walls begin deforming, sucking in all the Mages. In spite of their effort, Natsu and Lucy are unable to reach each other and end up being separated, while everyone else begin to be trapped by the fortress, soon to be tranformed into Plutogrim. However, the Demons notice someone's presence and it is revealed that the only human that has escaped Alegria is Lucy. Looking around, Lucy wonders where she is and what happened, while Plutogrim rampages through Magnolia Town, destroying the Kardia Cathedral. Mard Geer then reaches everyone, including Lucy, through Telepathy, to have the Tartaros' soldiers hunt after the girl for promotion as a prize. It is at that moment when a stream of water flowing out of Plutogrim hits Lucy and she gets swept away, soon to be found by the first group of Tartaros' henchmen.
While using a wooden board to stay on the surface of water, Lucy witnesses several soldiers going after her and uses Fleuve d'étoiles to fend them off. As more are coming, shooting beams of energy out of their weapons, Lucy takes advantage of her whip and maneuvers in order to evade and delivers a kick to the attackers. She proceeds summoning Sagittarius who defeats several more soldiers, until Lamy appears, proving that Sagittarius' arrows are ineffective against her Slippery Curse and thus Lucy summons Virgo instead to face the female Demon. An appearance of the maid seemingly annoys Lamy, claiming that her and Virgo's characters overlap, much to the Spirit's surprise.
At that moment, both Virgo and Lucy notice someone nearing their location and Lucy summons Loke to block Torafuzar's incoming attack. The Demon is surprised to have his katana parried by bare hands, even though Loke takes some damage. Lamy is pleased by Loke's appearance and Virgo questions the similarity between their characters one more time. Lamy then requests Torafuzar to let her deal with Lucy, however, Torafuzar simply states that he's going to carry out his duty and proceeds attacking Loke. Lucy begins showing signs of exhaustion and thus, knowing how much of Magic they take, Loke and Virgo are determined to defeat their opponents as soon as possible. Much to their horror, a third enemy, Jackal, approaches Lucy. Even though she wonders how it is possible that Jackal is still alive, Lucy decides to face him on her own and attempts to tie him up with her whip.
However, Jackal simply smirks, remarking that Lucy has probably forgotten about his Bomb Curse and proceeds using it, almost causing her to fall off the wooden board. Lucy questions her friends' whereabouts, but Jackal replies with more explosions. Torafuzar tells him to stop playing with his target, however, being under the impression that Natsu and Happy are dead, Jackal wants to torture Lucy for a little longer. She falls down to water as Jackal continues throwing explosions, however, Lucy soon grabs her chance and, much to the horror of Loke and Virgo, attempts to summon the third Spirit. As Aquarius appears, Virgo exclaims that Lucy's body cannot take three Spirits at the same time. Exhausted, but happy to see Aquarius' arrival, Lucy stands back as Aquarius makes full use of her Water Magic to sweep Jackal away. Virgo and Loke beg Lucy to close one of the gates while she can, however, at the same time, Torafuzar approaches Aquarius, claiming water to be his specialty, and slashes the Spirit. Before Loke and Virgo can help, they are ambushed by Jackal, who uses his Curse to deal enough damage in order to send them right back to the Celestial Spirit World.
Lying on the ground, Lucy is approached by Lamy and Jackal, who, knowing that she's out of Magic, want to torture her more, in spite of Torafuzar insisting that they finish her off immediately. Thinking that she cannot let it end like this, Lucy is hit by Jackal's explosion one more time and expresses her pain, much to Jackal and Lamy's amusement. Torafuzar tries to stop this, however, Jackal threatens him, so the Demon decides to take a leave. Lamy then grasps Lucy's arms to give Jackal a perfect target, but Jackal instead grabs Lamy's face and blows her up, laughing that she is annoying. A disgusted Lucy states that Lamy was his comrade, but Jackal grins that Lucy should instead worry about herself, when, suddenly, he is hit by a wave of water and Aquarius appears to hold Lucy while controlling the water to sweep Jackal away.
Aquarius then states that all she can do is to keep the Demon at bay, however, she reveals a way to defeat him, something that is possible for those who can open 3 gates at once: summoning the Celestial Spirit King. Aquarius continues by saying that he is the strongest being from the Celestial Spirit World, but Lucy argues that she doesn't have his key. Aquarius says that there is no such thing and reveals that to summon the Celestial Spirit King, Lucy has to break one golden key. Shocked, Lucy refuses to lose any of her Spirits, but Aquarius continues, saying that it will work only if there is a bond of trust between the master and the Celestial Spirit. She then insists that Lucy breaks her key. Lucy, however, despises the idea of sacrificing one of her comrades and tries to look for another way to solve the situation, but Aquarius states that she won't die, they just won't meet ever again. While Jackal tries to resist the water in order to reach the two, Aquarius states that she has always hated Lucy for being a complete opposite to her mother. Lucy brushes it off, calling Aquarius her first friend, but Aquarius exclaims that this is the only way to save her friends. Crying, Lucy goes with the plan and before Aquarius disappears, she realizes that not seeing Lucy again will be very lonely. She thanks Lucy just as the key is destroyed and Aquarius vanishes. Instead, the Celestial Spirit King appears, crashing through Plutogrim just to arrive to Mard Geer's location in order to face him.
The Underworld King expresses his surprise that someone is capable of summoning the Celestial Spirit King. The latter then questions Mard Geer's purpose and after hearing that Lucy was hurt for Tartaros to revive E.N.D. and reunite with Zeref, the Celestial Spirit King swears that he will defeat her enemies. The two begin their battle, with Mard evading Celestial Spirit King's sword until he manages to land his Thorn Curse. However, the Celestial Spirit King destroys Thorns with ease and proceeds using Meteor Blade. In spite of destroying great area with his strike, the attack misses Mard. Meanwhile, Jackal attempts to attack a crying Lucy, but much to his shock, his Curse is repelled by a shield of water. Lucy soon realizes that the Celestial Spirit King has given Aquarius' power to her and after hearing his words of encouragement, she stands up to face Jackal. The Demon attempts to throw more explosions to Lucy's way, but she continues to be protected by water. Walking forward, Lucy chants the incantation and hits Jackal with the full power of Urano Metria.
Jackal falls down, defeated, and Lucy, having used up all of Aquarius' Magic, follows him shortly afterwards. Meanwhile, Mard Geer and the Celestial Spirit King continue their stand-off, with the latter's movements getting slower, which is happily noticed by the Underworld King. Mard's thorn projectile is effortlessly blocked by the Spirit's sword which he then raises to cast Galaxia Blade. As a ray of light falls down, Mard is surprised to see a full frontal attack and then smirks, asking if the Celestial Spirit King is fine with Lucy becoming the collateral damage. The Celestial Spirit King returns the smirk and a shocked Mard realizes that instead, Alegria has been dispelled. While slowly vanishing, the Celestial Spirit King explains that this attack destroys darkness. He states that he will leave defeating the Demons to Fairy Tail Mages and returns to the Celestial Spirit World while Mard, giving a last warning that the malice for all humankind won't be forgotten, turns into stone.
Meanwhile, the Fairy Tail members are being released from Alegria. Erza charges at Minerva and the two clash one more time, much to the Demon's happiness. At the same time, Torafuzar returns just to find Jackal and Lamy defeated. Shocked and not knowing what kind of Magic Lucy used to accomplish this, Torafuzar aims to kill her, but is intercepted by Gajeel. While the Demon is unable to believe that there are more humans still alive, Keyes appears to take Gajeel down, but this time, Juvia blocks the attack with her Water Nebula. More faces arrive as Silver attempts to freeze his opponents, but his ice is cancelled out by Gray. One more Demon, Tempester, appears, covering the battlefield with flames that are eventually eaten by Natsu who arrives to assist his guildmates. Praising Lucy for saving them, as well as his opponents for their power, Natsu states that he's fired up, ready to face the Demons with the rest of the Fairy Tail Mages.