Luka returns as the protagonist of Monster Girl Quest: Paradox but things are not as they once were.
For starters, monsters and humans have been living together in relative peace since the Great Disaster thirty years ago so his dream of becoming a hero to foster co-existence between them has never even occurred to him. While he still desires to be a hero, his immediate concern is to go out and look for his father, Marcellus, who is still alive in the world of Paradox.
The gameplay focussed nature of Paradox and its focus on other companions has left little room for Luka's personality to shine through albeit he has differences from the original trilogy. For instance, he studied mathematics to take care of his inn which impresses even Promestein. More remains to be seen but for now, he appears to be the same naive hero from the first game. However, because of some of the choices available in the game, it's possible to play Luka as more lecherous or irresponsible, but he still comes across as an idiot.
Luka possesses a new ability in Paradox, which allows Luka to travel between the dimensions, that hints there might be something more to his lineage, this time around, but that is mere speculation at this point based on an end-game spoiler.
As revealed in Catalyst chapter Heinrich's wife was Edena the princess of Remina tying Luka's lineage with the royalty of Remina making Luka also royalty.
Luka has a vision in which Ilias warns him of a danger that will swallow the world. However, much of the vision is obscured by a static effect (later revealed to be Apoptosis, and Luka is unable to gain much information.
When he wakes up, Luka thinks that the vision was just a normal dream, albeit a good omen. He recalls that Ilias hasn't been seen since the Great Disaster thirty years ago. He says that today is the day that he will be baptised as a Hero and go out on a journey to find his missing father Marcellus. Suddenly, there is a commotion outside. Luka runs out and learns that Hans, the lumberjack, was kidnapped by an evil slime girl. Against the advice of his fellow villagers, he heads for Slime Mountain to rescue Hans.
While climbing Slime Mountain, Luka and a friendly Slime Girl hear a loud crash. Luka finds that a crater with a young angel lying in the middle - a younger version of Ilias. Luka doesn't believe her claim of being Ilias, for which she ineffectually shocks him. Stunned at her weakened state, she speculates how it could have happened. Eventually, she runs off, telling Luka that they will talk again later.
At the summit of the mountain, Luka fights a Bunny Slime and two Slime Girls to rescue Hans. Hans returns to the village on his own.
While heading back down, Luka runs into a young Yoma with the form of a Lamia - a younger version of Alice. She asks if he's seen a rabbit anywhere. If Luka answers no, she doesn't believe him and continues blocking the path. If he answers that he's seen one at the summit, Alice thanks him and goes there. Luka decides to check on the situation and finds Alice beating up the defeated Bunny Slime. Luka intervenes, and Alice realises that the Bunny Slime isn't the rabbit she's looking for, so she leaves. Luka returns to the village.
Return to Iliasville
When heading to the temple for his baptism, Luka is accosted by his childhood friend Sonya (a temple priestess) for being late. They rush to the temple and meet the Head Priest for the baptism. Although the baptism has been purely for show in recent years, due to Ilias' disappearance, this time Ilias does descend. Ilias tells Luka that a darkness is covering the world and Luka is the only one who can stop it. She lacks the power to baptise Luka, but says that he will nevertheless be up for the task as an unblessed hero. After Ilias vanishes, the three of them discuss this matter and agree to keep it a secret to avoid mass panic. Sonya leaves, only to hurry back and tell Luka that two children are fighting in his house.
In Luka's house (the village inn), Alice and Ilias are fighting and Luka has to force them apart. They tell him their true identities, which Luka naturally is skeptical of. Both of them are unable to contact their subordinates and are searching for answers about their current states. They ask Luka to join them, Alice because he's the only adventurer leaving the village at this time and Ilias because she's aware of his true lineage and potential. Since they are mortal enemies, Luka can only choose one of them. When Luka chooses one of them (hereafter referred to as Alice/Ilias) the other one (hereafter Ilias/Alice) leaves in a huff. Luka and Alice/Ilias explain their situations to each other.
The pair leave the inn and head to the Village Chief's house. The Chief gives Luka information about recent history and the current state of the world. When they leave the house, Luka and Alice/Ilias meet Sonya, who has been planning on accompanying Luka and forces herself into the party. She is also skeptical about Alice/Ilias' true identity. A strangely-dressed traveller, Nero, approaches and talks to the party. He claims to just want to wish Luka luck on his travels, but is confused by the presence of Sonya (saying that Luka shouldn't have a childhood friend) and by the prevalence of magic in the world. He leaves, with the party just as confused by him.
There is a Slime Girl, Lime, trapped in a poison marsh on the east side of the village, whom Luka proceeds to save. Lime then joins the party.
Immediately after leaving the village, Alice (if recruited) attempts to give the Angel Halo to Luka so he can fight without worry of killing his opponents. If this happens, Nero stops time and steals the Angel Halo. Regardless, Alice/Ilias will present the Pocket Monster Lord's Castle as a mobile base (Ilias mentions stealing it from Alice during their struggle).
The party first heads for the large town of Iliasburg. Along the way, they camp for the night. Alice/Ilias teaches Luka a skill, while Sonya describes a past incident in which Luka saved her when she was lost.
At the entrance to Iliasburg, the party runs into the White Rabbit, the rabbit who Alice talked about earlier. She is evasive as to her purpose and eventually disappears, leaving the Key to Hades behind. Only Luka is able to see the key, the others remaining entirely unaware of its existence.
The party searches for information on the White Rabbit and is directed to an information broker named Amira. However, they learns that she was kidnapped by a gang of bandits. After defeating the bandits (who turn out to just be monster children and are allowed to become part of the town after they apologise for their crimes) it turns out that Amira wasn't kidnapped after all. She does have information about the White Rabbit, but can only reveal it if paid (since she is an information broker) or if the party completes a sidequest to become information brokers. They eventually learn that a rabbit was seen in Pornof.
The Hunt for the White Rabbit: Part 1
The party goes to Pornof but learns that the rabbit in question is just an ordinary Rabbit Girl. She does, however, mention hearing about the White Rabbit in the nearby Tartarus.
The party explore their first Tartarus, a mysterious cavern filled with Apoptosis monsters. At its depths is a strange door, which most are unable to even budge but which Luka can open with a touch. On the other side is a twisted replica of the city of Remina, which was thought lost in the Great Disaster. However, its citizens are not human but more Apoptosis. In one house, the party finds a strange monster resembling a scylla, who attacks the party out of surprise. After defeating her, she wants to join the party and is accepted. Sonya gives her the name Nuruko.
Continuing through Remina, the party finds a magic circle which takes them at the exit of what initially seems to be the same Tartarus. The White Rabbit appears and warns them not to step off the path (as powerful and hostile angels are present). The party discovers that Iliasville has been utterly destroyed by the angels, with all inhabitants killed. They find Luka's diary in the now-packed graveyard, which reveals an alternate timeline in which Granberia appeared in Iliasburg and caused him to give up his journey. The final entry, written by someone else, mentions that Luka fought heroically against the attacking angels. Alice/Ilias attempt (unsuccessfully) to use a Harpy Wing, then tell Luka to do it. The item functions in his hands, taking the party back to their world (henceforth the "Paradox world". As a result, the party is now aware that the Tartarus are passages between alternate worlds.
The party passes through several villages and fixes various problems. A notable case is the mysterious disappearance of the harpies.
While investigating Harpy Village, entirely devoid of its inhabitants, the party runs into Nero again. He explains that the harpies contracted a supposedly-extinct virus and voluntarily quarantined themselves. He hands over a Yggdrasil Fruit for the party to use to cure the harpies. They succeed in doing so (though they don't have enough fruit to cure the queen). A harpy later explains that their queen met with some strange and powerful succubi before the plague started. The succubi were called Lilith, Astaroth and Morrigan, the names of the legendary Lilith Sisters who were thought to have died long ago. Sonya hypothesises that the succubi were carriers of the virus and accidentally spread it to the harpies.
In the Paradox World, the village of Rostrum is a ruin where none live. Nearby is a Tartarus, which the party explores. In the Remina on the other side, they find an angel scholar, Promestein, who was mysteriously transferred here and has been trapped ever since. She learns of Luka's ability to open the doors between worlds and joins the party, eager to uncover the secrets behind this ability. The world on the other side of the Tartarus turns out to be set at an earlier time than the Paradox world, with Rostrum still a thriving village. Here they find that Marcellus had earlier visited and left a letter for his son Luka, despite the Marcellus of this time not having any children yet. The party deduce that the Marcellus who left the letter must be the one from the Paradox world. The letter tells Luka to go to Enrika and ask someone called Micaela for help.
The elves and angels who inhabit Enrika are initially wary of the party. One elf, after hearing that Luka is looking for Micaela, breaks down in tears. She explains that Micaela left the village over two weeks ago and warned that, if Luka ever came looking for her, that meant that she must have died. The elf also explains that, with Alice XVI's sealing and disappearance from the public eye, the monsters are undergoing a succession crisis. Three candidates are vying for the position of Monster Lord: Alice XV, Alice VIII, and Alice XVII.
The party heads to Ilias Port, planning on taking a ship to the Sentora Continent. However, mysterious storms are preventing any ships from travelling between the two continents. Nero appears again and tells the party to go to the Cave of Treasures to obtain the Poseidon Bell, an artifact that will let a ship sail in any weather.
In the Cave of Treasures, the party runs into Nanabi, the aide of the Heavenly Knight Tamamo. Nanabi refuses to let them pass and proves too powerful to defeat, only for Neris to intervene and defeat her easily. Someone who looks like Tamamo walks in, but Neris explains that it is simply a copy from another world. The White Rabbit appears and attempts to erase Neris, but Nero intervenes and the two of them disappear. Neris hits on Luka before leaving.
Ship to Sentora Continent
Thanks to the Poseidon Bell, the ship the party takes is unaffected by the storms. However, Morrigan, the one responsible for the storms, notices and attacks. The party defeats her but only due to her holding back, and she threatens to kill them all, despite the potential consequences. Then Zion, a Seraph-ranked angel who Ilias does not remember creating, attacks and engages Morrigan in a fight. The ship sinks as a result of the fight, and the party is rescued by mermaids who take them to Port Natalia.
In Port Natalia, the party learns that mermaids and fishermen have been going missing. They investigate and learn that Astaroth is responsible for this. Astaroth defeated Kraken and drained her into the form of a dried squid, then brainwashed the mermaid Meia into thinking she was the Queen of the Southern Seas and causing her to kidnap fishermen and jail any mermaids who came to investigate.
The next destination is the religious city of San Ilia. Upon entering the castle, it turns out that the Ilias Temple had sent ahead a message advising the leaders of the faith of Luka's unique baptism, and he is allowed in as a special guest. The King of San Ilia reveals all the relevant information he has, including that Marcellus was seen entering the library of the castle. It turns out that Marcellus left a book there, containing a letter advising Luka to form contracts with the Four Spirits. The King also requests help from the party, though they first need to visit the Holy Mountain Amos to get mithril to improve their equipment.
On the mountain, the party encounters Ilias/Alice who are unnerved at a presence at the summit. At the summit, they find a dying Micaela and another strange Seraph, Gnosis. Gnosis does not attack as it would accelerate the spread of Chaos, and leaves. Micaela uses the last of her power to baptise Luka as a Hero.
Now properly equipped, the party accepts the King's request. They escort him through the Ancient Temple Ruins to the devices he needs to perform maintenance on his cybernetic body. At the same time they encounter the gynoid Brynhildr, whom Luka awakens by accident. After she attacks and is defeated, Brynhildr is convinced to join the party as they have a common goal in saving the world.
The party visits a Haunted Manor overrun by zombies and ghosts. They defeat the necromancer responsible for the mess, Chrome, and convince her to stop experimenting with the dead. She agrees to join the party when they bring her the Magical Thread that she needs to practice puppetry.
The party visits the Forest of Spirits, where the spirit of wind, Sylph, resides. They hear about a strange but non-hostile monster roaming the forest. After Luka forms a contract with Sylph, the Armored Berserker attacks. He is too powerful to defeat, but Nero and Neris come to the rescue. Neris teleports away with the party while Nero defeats the Berserker. Luka has a vision of Micaela telling him about his mother being an angel (an event in the original game) and thus awakens his angel powers. He wakes up in the Pocket Monster Lord's Castle, where his companions discuss recent events.
While travelling to the Safina Region, the party finds a mysterious tower inhabited by Kagetsumugi, a legendary puppeteer. Alice/Ilias hurries Luka away, warning against getting involved with Kagetsumugi. They therefore do not learn of Kagetsumugi's alliance with Black Alice.
The party travels to the city of Sabasa and learns that its new queen Sara is neglecting her responsibilities and living a life of debauchery. After a meeting with the rebel assassin Salaan they learn that Sara's monster blood was awakened, partially turning her into a succubus. With the help of Sphinx, they restore Sara's sanity by fully turning her into a succubus. A soldier then bursts in with news that Luddite Village is under attack by succubi.
Returning to Luddite Village, the party finds that the Lilith Sisters have seemingly massacred all of the inhabitants. Astaroth stays behind to fight the party while her sisters leave. After a fight in which Astaroth holds back her true power, she says that Luka may be able to help the Lilith Sisters with their objective and then leaves.
Back in the Safina Region, there is a civil war in Witch Hunt Village. Luka must decide which of the two sides to ally with. The leader of the victorious faction (either Lily or Lucia joins the party.
In the casino city of Grandeur, the party puts an end to the seduction of the inhabitants by the succubus idol Saki. They also find Merlin, one of Marcellus' old friends, now the apparent Don of the Mafia. After the party leaves, Lazarus crawls out from under the table and is revealed to be the actual Don.
In the Safar Ruins, Luka forms a contract with the spirit of earth, Gnome.
The party enters the third Tartarus, using Gnome's power to get past an obstacle that the White Rabbit had left at the entrance. Here, they find signs of Chaos eating into space itself. The world on the other side is in its death throes. The party makes its way to the last bastion, the Administrator Tower. Even here, there are no living survivors, only undead and artificial monsters.
The tower's owner, La Croix, explains how Chaos is consuming this world and will eventually consume them all. She gives the party her notes and makes them leave for their own world. La Croix stays behind to hold off Adramelech, a powerful Apoptosis who invades the tower.
But Adramelech is able to intercept the party before they can escape. They defeat her with great effort, but Adramelech grabs onto Luka and is on the verge of pulling him into the void. Marcellus appears and cuts Adramelech in half. He advises Luka to protect his world and leaves.
Back in the Paradox world, Luka and his party reflect on what they've learned. They resolve to find some way of stopping Chaos.