Magic-user/elf Lefiya of the Loki Familia is upset with herself that she is unable to be of more help to her comrades, especially to Sword Princess Ais Wallenstein, whom she carries a crush for. While expeditioning on the 50th floor of the Dungeon, the Loki Familia are attacked by a hoard of poisonous caterpillar monsters, which disintegrate anything they touch. Lefiya tries to cast a magic spell on them, while fighters Tiona, Tione, and Bete keep them busy, but panics and is unable to finish the spell, leaving Ais to jump in and easily take them out with her wind magic. With the 51st floor currently blocked off due to the fight, the Familia head back to Orario to regroup. On their way out, a hoard of minotaurs suddenly appear and start escaping into the upper floors. One of them attacks a lone adventurer, which Ais steps in to defeat, saving him. The speechless boy runs away scared, while Bete looks on laughing, with Ais all the while confused at the boy and annoyed at the laughing.

Returning from the expedition, the Familia is greeted by Loki, who proceeds to try to grope all the girls, with Lefiya unable to escape. Knowing that Ais has her own issues she's dealing with, Lefiya wants to do something to try to help her, like giving her some gifts as good luck charms. Ais starts to feel restless with herself that she still hasn't surpassed Lv. 5 yet. That night, while celebrating at the tavern, Bete starts joking and insulting about the boy Ais saved from the minotaur, upsetting her. The boy, Bell, overhears all of this and storms out of the tavern, distressing Ais even more. After confiding in Riveria that she wants to apologize to him, Tione, Tiona, and Lefiya take her out shopping to try to cheer her up, buying her a dress she likes. Realizing what Lefiya's been doing for her lately, Ais apologizes and thanks her for everything and for caring about her.

At a banquet for the Gods at Ganesha's, Loki converses with Dionysus and Demeter before running off. While training in the Dungeon with Ais, Lefiya asks her on a date to the upcoming Monsterphilia, which she accepts; Loki later states that Ais will be going with her to it as her escort, crushing Lefiya. Loki and Ais meet up with Freya, who reveals someone from another Familia has caught her attention and wants Loki to play along with whatever plan she's cooked up, before abruptly leaving. As the event starts, Freya unleashes several of the monsters to cause havoc, which Ais heads out to deal with. Tiona, Tione, and Lefiya follow suit, but are all distracted by surprise plant monsters that start attacking the courtyard. Despite being knocked out and badly injured, Lefiya stands back up and successfully executes her summon boost spell, completely freezing the enemies. That night, Loki questions Freya about why she summoned the monsters, only to learn she had nothing to do with the plant creatures that attacked them. Outside, Dionysus, holding one of the plant crystals, looks on and smiles.

An adventurer in Rivera shares a bed with a red-headed woman, only to be choked to death by her. That night, Ais has a dream about her mother and father. Obtaining a huge sum of debt from a sword she broke, Ais prepares to head back into the Dungeon, with most of the core Familia following along with her. Bete stays behind as Loki's escort to investigate the sewers beneath the city, where they uncover more of the plant monsters. Along with recognizing the magic stone being similar to that of the caterpillar monsters, Bete notes the scent in the sewers is the same as Dionysus, whom they run into. Dionysus reveals to Loki he was investigating the monsters as well, saying he believes Ouranos to be responsible. Arriving in Rivera, Ais and her group discover about the murder and offer their assistance in uncovering the mystery. Finn deduces the person is still in town, so they start inspecting everyone, where Ais and Lefiya notice a mysterious faun girl running off. The girl, Lulune of the Hermes Familia, reveals she is in possession of a package given to her by the murdered man, as part of a quest by another mystery person. Discovering it to be an orb with a creature inside, Ais starts to freak out and hyperventilate, while a scarred man looks on and summons more plant monsters.

As Rivera is under attack from the plant monsters, Ais, Lefiya, and Lulune are cornered by the scarred adventurer. Ais figures out they are actually the murderer, wearing the face of the adventurer as a disguise. The red-headed woman fights with Ais, trying to reclaim "the seed", and after seeing Ais' wind magic, the woman refers to her as "Aria", shocking Ais. The seed, reacting to her wind magic, fuses with a plant monster and evolves into a giant woman-looking creature. Meanwhile, Loki confronts Ouranos about what's been going on, with him standing firm that the Guild isn't responsible. As Loki slyly leaves, his assistant, Fels, states that someone must've instigated this, and pushes Ouranos not to make an enemy of Loki. Ais finds herself completely outmatched by the woman, but is saved thanks to the rest of the Familia, and unable to match against Finn and Riveria, the woman retreats. Unable to find anymore leads, the Familia head back home, while Ais has another dream about her mother, Aria, and her father leaving her. Starting to feel even more reckless, she decides to stay in the Dungeon for a while to train, with Riveria reluctantly staying back to watch over her. Running into the Floor 37 boss, Ais stands her ground to face it alone.

Still distressed over losing the last fight, Ais pushes herself to keep getting stronger. Despite Riveria's attempted assistance, Ais pushes through and manages to take out the dangerous Floor 37 boss all on her own. After being scolded by Riveria, Ais tells her about the red-headed woman calling her "Aria". In response, Riveria reminds her that everyone in the Familia is her family and are always there for her. On the way back, the two discover an unconscious Bell on the floor of the Dungeon; Ais stays back to try to apologize to him. Comforting and giving him a lap pillow, Bell awakens, and too embarrassed, rolls away before she can apologize, to her annoyance. Flustered over this, she goes to see Loki to get a status update, where they are shocked to discover that Ais has finally jumped up to Level 6, which Ais herself isn't sure exactly how to react towards. While preparing to head back to the Dungeon, Ais runs into Guild worker Eina, who thanks her for assisting Bell, to Ais' pleasure. Overhearing some other adventurers talking about Bell falling into a trap, Ais runs off after him. She finds him cornered by monsters, baffled at his sudden magical abilities and rapid growth in strength. She takes out the rest of them, but is unable to apologize before he once again runs off. After picking up his lost equipment, she is startled by Fels, who reveals he gave the original quest to Lulune, and asks for her help for a new quest.

Fels tells Ais about a monster outbreak on the 24th floor and wants her to investigate, requesting her due to the possible connection to it and the red-headed woman she fought; Ais accepts. Dionysus, also aware of these rumours, informs Loki about Ouranos' possible connection. When she receives a letter from Ais about her quest, she orders Lefiya and Bete to head down there and help her; Dionysus has his right-hand, Filvis, also join them. In Rivera, Ais meets up with Lulune and the rest of the Hermes Familia, who are assisting in the quest. Arriving on the 24th floor, Ais and the group discover the source of the monster hoard, which Ais takes out with ease thanks to her level up. In the pantry, they learn the monster's food source has been blocked off by a plant-like chrysalis. Entering it, they are attacked and separated by the red-headed woman and another masked figure, who have been controlling it and watching over them. Meanwhile, heading down the dungeon, Lefiya tries to converse with Filvis but finds her unresponsive and closed off. Making it to Rivera, the three of them learn from a shopkeep Ais met with earlier about her location. He also tells Lefiya to stay away from Filvis, referring to her as "the Banshee", a cursed adventurer in which everyone she's ever partied up with has died.

Lefiya and the shopkeeper talk about the "Nightmare on Level 27" in which adventurers were led into a trap by the vicious Evilus factions, led by Vendetta, leaving Filvis as the only survivor. Due to every other time she's partied up with others all ending in tragedy, Filvis has gained the distinction as a cursed adventurer. While Bete confronts her about always running away from her problems, Lefiya shows up disregarding all the comments, insisting she continue to help them, and complimenting her on her beauty. Blushing, she thanks her and agrees to keep going. The red-headed woman, Revis, and Ais engage in combat, with the former annoyed at the latter's clear boost in strength and rank up. The Hermes Familia take on the masked figure and his giant plant monster, finding themselves completely outmatched until Lefiya, Bete, and Filvis show up in time for backup. The man, who is unveiled to be a resurrected Vendetta, now powered by a monster crystal of his own, reveals he's been creating these monsters with the purpose of driving out all the other dungeon creatures so that they may lay waste to Orario, all to serve a mysterious God woman he begins raving about. As the fighting continues, Ais and Revis' confrontation reconnects them to everyone else. After the main monster is destroyed and Vendetta is knocked out, Revis shows up killing him herself, devouring his power crystal to make herself stronger. With the room starting to cave-in, everyone makes their escape out, while Revis tells Ais to go to Level 59, which is where she will find what she is looking for. Several days later, the Loki Familia captains set their plans for a grand expedition down towards said floor. At the same time, Lefiya, Tiona, and Tione look through the library where they find a book, "Dungeon Oratoria", learning Aria was a Spirit, a magical being most beloved by the Gods.

As the Loki Familia prepare for their big expedition to the 59th Floor, Ais goes to see Eina for one last attempt to apologize to Bell. He shows up and they manage to stop him before he runs away. She finally apologizes for scaring him off all those times, and he apologizes for always running, thanking her for all the times she saved him. Ais offers him training to learn how to properly fight, while also intending to learn what causes him to improve so fast. Lefiya, wanting Ais' assistance to train, chases after her early the next morning, only to run into Bell, who quickly escapes after realizing she's also looking for Ais. She eventually spots Ais and Bell getting close, causing her to get depressed. That night, Ais tells her she's just training him, leading her to be relived, while still jealous, so agrees to keep it a secret if she also trains her as well, which Ais accepts. The following morning, Lefiya sneaks up to their training session, where she spots Ais giving Bell a lap pillow, to her shock. During their sparring session, Lefiya's unable to keep up with Ais' strength, but refuses to stop so she can keep up with Bell. The following day, she's annoyed that Ais will be spending the whole day with Bell, until she runs into Dionysus and Filvis, who after seeing them getting flustered with each other, recommends they go training in the Dungeon together. Filvis helps her improve her concurrent chanting for defence, and promises to help her more when she returns. While training with Bell, Ais asks him how he got so strong so fast, and he says there's someone he'll do just about anything to catch up to. Ais understands this, thinking back to losing her mother and father at a young age and wanting to help them. That night, they are surprised by Hestia, Bell's goddess, who shows up to console and comfort Bell. Walking back home, the three are suddenly attacked by masked fighters.

Ais defends herself against the masked fighters, who tell her to stay out of their Lady's way, before leaving. As Bell and Hestia head back home, she realizes the attackers are from the Freya Familia, but unsure about what they could want, with Loki hinting Ais might be getting involved in something Freya wants. Lefiya continues her training with Ais, which she thanks her and Filvis for how fast she's been able to improve herself. She runs into Bell again in the streets, telling him she's not going to lose. Ais and Bell conclude their training sessions, thanking and wishing each other good luck. On the day of the expedition, Ais sees Lulune again, who gives her a special charm she received from Fels. Joined by the Hephaestus Familia, the adventurers make their way in the Dungeon, when suddenly another group show up talking about a giant minotaur roaming the 9th floor, attacking a white-haired kid. Knowing it's Bell, Ais immediately dashes forward after him, only to be stopped by Ottar, Freya's second-hand, who challenges her to a duel. Realizing this is what the attackers warned her about, she tries to fight but is unable to get through his defences. The rest of the Loki Familia show up to assist, allowing her to escape; Finn gets Ottar to leave when he questions him about his and Freya's motivations. Ais once again shows up to save Bell, but he pushes her aside to take on the minotaur himself. They all look on in awe at his strength and abilities, as he manages to keep up and kill the beast, with Ais commenting to herself that he has the look of a true hero. Ais returns the unconscious Bell back to Hestia, as her and Riveria wonder what else is waiting for them.

Resting on the 50th floor, the Loki Familia finds themselves all hyped up and excited for the upcoming battles, inspired by Bell's fight with the minotaur. Lefiya feels jealous over hearing about all this, but still aims to keep up and assist her friends as much as she can. The core Familia members push their way through the next couple floors and the hoards of monsters and traps, until Lefiya is knocked down one of the holes. Bete, Tiona, Tione, and Gareth join her in free falling down towards the 58th floor to face against all the dragon monsters, while Ais, Riveria, Finn, and the rest take the long way down. Revis continues consuming more power crystals to get stronger, while arguing with a masked being watching over her. Ais' group catches up to the rest, and after taking out the remaining beasts, prepare to head into the unexplored Floor 59. Through the normal looking jungle environment, they tumble upon a plant monster feasting upon other caterpillars, when it suddenly transforms into a woman-looking creature, which Ais identifies as a Spirit after it calls her "Aria".

Confronting the beast, the Loki Familia figure out the reason behind the creation of the plant monsters was to act as a source of magic to power the Spirit. The being calls out for "Aria" as the next thing she wants to devour. The Spirit starts chanting incantations, blocking all forms of magic and attacks and decimating the group with several destructive blows. All seems lost until Finn makes a stand, using Bell to inspire everyone not to give up and keep fighting. They all work together to push through each of her defences, physical and magical, until Ais gets right up close to take the final blow. As the Spirit is about to hit her with a direct spell, Lefiya manages to send out another spell quickly to block it, allowing Ais to achieve the hit with her wind magic, completely destroying the Spirit. The group celebrates their success before eventually going back home. Meanwhile, Ouranos reveals to Fels that the Spirit was just the emulation of a deceased spirit, used as a decoy to hide the real threat on a much lower floor, claiming this to be the work of Enyo, a being that wants to completely destroy Orario. Revis sits back in contempt, stating she'll continue to get stronger, while Dionysus and Filvis also hear about Loki Familia's return. That night, Ais thanks Lefiya for saving her in the fight, while she thanks Ais for always being there for her. Loki shows up to once again try to grope the girls, but this time Lefiya manages to defend herself, getting praise from the others.