The game begins in Hades, where Valvatorez, a former tyrant, is training the next batch of Prinnies in Hades. Fenrich, his loyal servant tries to give him a sardine with human blood but Valvatorez refuses to drink any human blood due to a promise made in the past. They are called down to give the Prinnies their last lesson before they graduate the course. After the final lesson, Valvatorez promised to give each Prinny a sardine and just before they could eat it, a vortex appears and takes them away.
Noticing that this is an action of the Corrupternment, Valvatorez decides to rescue the Prinnies and give them the sardines as promised. They go on to meet Axel, who is now a warden at Hades tells him that he cannot hand over the Prinnies to them. Having no other choice, Valvatorez and Fenrich fight Axel and afterwards, the Corrupternment sends a group of assassins called the Abanddon to quell the uprising in Hades. Axel escapes and tries to tell the Abanddon that Valvatorez is behind the uprising but Fenrich convinces the Abanddon that Axel is behind it. He is forced to fight with Valvatorez and is told by him that he should not side with the Corrupternment. The leader of Abaddon reveals himself as Emizel, the President's son to them. Axel tries to suck up to Emizel but he doesn't believe him and strikes Axel.
Thinking he was killed, Valvatorez fights Emizel and wins, causing him to be embarrassed and sets free the Prinnies. However, a girl named Fuka appears and states that she will annihilate the Prinnies and declares a war. Valvatorez is disgusted at the thought of it but Fenrich tells him that she is foolish and plans to stop her. They go to a heavily polluted area, filled with waste from the Human World. Noticing that the Corruptement is letting this happen, Valvatorez wonders how far it has fell.
It is revealed that Fuka was meant to become a Prinny but the Prinny Factory ran out of skins and gave her a Prinny Hat and Jacket. She thinks by eliminating the Prinnies, she will improve her working conditions when Valvatorez says that she must follow the path of a Prinny. Fuka believes it is all a dream as she did not want to believe that she had died and became a Unprinny. She reveals her secret weapon which turns out to be Emizel but Fuka finds out from them that he is weak and is defeated again. Later on, Fuka decides to fight them herself and Fenrich notices that she has a power comparable to demons. They defeat her and Fuka wonders why she had lost in her dream and why her "nightmare" won't end.
Valvatorez asks why and Fuka states while she doesn't have to go to school, she has to live through the harsh working conditions of a Prinny when he tells her that's how Prinnies live. She runs away to the most polluted area filled with monsters afterwards. Fenrich tells Valvatorez not to rescue her but he states it is his duty as a Prinny Instructor. They catch up to her and Fuka learns why Valvatorez came to rescue her and joins the group before fighting a group of slimes. Out of nowhere, Axel appears to them alive, stating that he has released of all the prisoners in Hades and tells them that if they kill Valvatorez, they will be pardoned.
In Hades, Valvatorez goes to contain the prison break with Fuka following along. Some prisoners reveal that they were imprisoned for trying to do their job of scaring humans. They learn that Valvatorez was a former tyrant and run away with Valvatorez questioning if demons are doing their jobs to obtain fear energy. With the prisoners being unable to defeat Valvatorez, Axel decides to unleash the forbidden prisoner. It is also revealed that Emizel is working with Axel to stop Valvatorez's efforts. At the Forbidden Cell, the prisoner is revealed to be Desco, a final boss in-training. Fuka states that Desco is one who put her into her dream and Desco sees that it is Fuka, her big sister. Desco states that she must kill the hero when Valvatorez states he is not one. Axel orders Desco to kill when Desco blasts Axel, making it look like he died again.
Desco decides to target Emizel next when Valvatorez moves to protect Emizel from her attack. The Prinny Instructor states to Desco what a true final boss must be and fights her. Being defeated, Desco tears up and asks is she is going to be abandoned again. She reveals that she was created by humans and seeing how demons are letting humans run loose, Valvatorez officially declares to ursurp the current reigme. He promises Desco to help become a final boss and she joins the party.
The Hades Party is formed, with several demons taking note. Emizel wakes up as he fainted after being protected by Valvatorez. Fenrich tells him to come with them and hands Emizel a newspaper, stating that he had died. In the fourth episode, Emizel wonders how they could publish the newspaper and wonders if his own father believes he is dead. Reading the newspaper, Valvatorez takes note of a spelling error, with Prinny being spelt as "Primy". He declares to go to the Information Bureau to correct the mistake when Fenrich reminds him of their primary goal of taking over the Bureau. Emizel decides to tag along and tell the Bureau that he is alive.
Before they depart, Fuka tells Desco that she isn't her sister when Desco tells her that she was created by her dad. Valvatorez breaks up the fight and states they must get along for the Party's bonds to be stronger. At the Information Bureau, they manage to sneak in due to Emizel knowing the security system. Seeing the security guards, Emizel tells them that he is the President's son and is alive. They don't believe him despite him showing a royal emblem as they believe everything in the newapaper. Meanwhile, a suspicious Prinny sneaks in with Desco asking who it is before the Prinny states that it is a worker.
At the top of the Information Bureau, the Chief appears and wonders how Valvatorez's party managed to get in. Emizel move forwards and identifies himself as the President's son and asks them to withdraw the newspaper. The Chief answers back stating that it was an order of the Corruptement and his father knew about it. Being confused, Emizel wonders how his father knew when Fenrich tells him that he sent a humiliating video of Emizel running away as blackmail. Valvatorez states that Emizel must not rely on his identify anymore and instead become a mature person with Emizel having conflicted emotions about it. Later, when the Chief is defeated, Valvatorez asks her to correct the spelling mistake when Fenrich steps in and asks her their true goals. The suspicious prinny from before walks in and fines the Bureau for damages done to Celestia.
Noticing its abnormal speech for a Prinny, Valvatorez asks it to identify itself and it reveals itself as the Angel of Avarice. The angel tells them her name is Vulcanus and makes off with the Bureau's money with Valvatorez wondering if she was a girl he had met before by the name of Artina. In Episode 5, Emizel asks Valvatorez on why is he so gloomy. Fuka walks up to Emizel and pulls him to where Desco is. She tells him that he is thinking about the angel and that she must be someone he had met before since he called her Artina. Desco adds on to the conversation thinking it might be love where Emizel thinks it's a crazy idea. Fenrich dismisses such ideas and tells Valvatorez not worry about the angel. They decide to go to the mid-level demon area in order to gain the support of the low and mid-level demons for the upcoming Evilection.
Appearing as an amusement park, Fuka and Desco are excited to go on rides together when Valvatorez and Emizel tell them that it is training course. Wanting to know the past of him and Artina, Fuka asks him for his story in the past. Valvatorez decides to share with them and tell them his past days of when he was a Tyrant. 400 years ago, as a tyrant, Valvatorez scared many humans and took as much blood as he wanted. During a human vampire hunt, he met Artina who wasn't afraid of Valvatorez when they first met. As she learned that vampires needed blood for survival, she offered Valvatorez her own blood but he refused as wants to scare her first. This led to a promise where Valvatorez promised to protect Artina so that he could scare her but refused to drink any blood before taking her own.
Back in the present, his story is interrupted by a group of demons when Fuka and Desco are angered for not hearing the end of the story. After defeating them, they move on to the next area where they see Vulcanus surrounded by group of demons wanting to kill her. Fenrich didn't mind them killing her but Valvatorez intervenes and saves Vulcanus. At first, she isn't grateful to them but says thanks to them. She asks why demons aren't doing their job of scaring humans before managing to escape. Valvatorez decides to tell the rest of the story to them afterwards.
After three days Valvatorez made the promise, Artina was killed due to her aiding wounded enemies of her country. Being at the scene of her dying breath, Valvatorez blames himself for not protecting her and is the reason why he does not drink blood 400 years later. As they arrive at a merry go round, they meet up with Vulcanus and learn that she is already on her way, presumably with the area's money in hand. Although Valvatorez does not see her as a threat, Fenrich decides to tempt her into fighting them by telling her that they have a 10 million HL bounty on their heads. Interested in the money, Vulcanus decides to fight them and Magichanges with two Catsabers in order to do so.
After she is defeated, Fenrich decides to turn her into the Corrupterment to receive the bounty reward on her head. He lets her have a conversation with Valvatorez about his duty in scaring humans and learns of his name. Noticing something was wrong, Vulcanus shields Valvatorez with her body from a bullet fired by Axel who is revealed to be alive. Later on, Vulcanus awakes, shocking Fuka as she presumed that she was dead. She decides to tag along with the group as she claims they owe her 5 million HL for saving Valvatorez's life.
The party decides to move on to the upper level demon area where it is a snowy graveyard. They notice that its inhabitants sound and act like Axel including Fuka, Desco and Emizel. Eventually, they catch word of the A-Virus, a virus that transforms its victims into Axels. As they progress through the area, Fuka, Desco, and Emizel slowly starts changing into Axels, beginning with an impersonation, followed by bodily changes such as chest hair growing on Emizel. Valvatorez promises them that he will find the cure, claiming that it can be found by defeating the area boss. Eventually, the real Axel appears to them, saying that the Corrupterment developed the A-Virus in order to suppress the rebellious inhabitants of the Netherworld.
Axel also claims there is no cure for the virus and later, they fight Axel. When he is defeated, it turns out that it was of no use and Fuka, Desco, Emizel and Fenrich all transform into Axel. Valvatorez is diswayed by this, stating that he will find cure and will never break a promise again. Vulcanus decides to injure herself to gather up her blood from her arm. She goes to Fuka and tells her to drink her blood, after Fuka drinks it, she restored back to normal with the rest of the infected being cured as well. Vulcanus explains that angel blood can cure any impurity but had not told them about this as it is against Celestian Law for an angel to injure themselves. She decides to go sell her blood to the remaining infected demons and the rest of the party decide to make their move, which is taking over the Corrupterment and defeating the President.
At the start of Episode 7, the party plans their final move on the Corrupterment, going into the Blight House which is the office of the President. Emizel states that the Corrupterment has 600,000 demons in the area and Fenrich responds with a plan to secretly invade the Blight House and assassinate the President. Valvatorez says that it is a cowardly strategy and they must take on the Corrupterment with full force. They arrive at the entrance to the Corrupterment and Valvatorez states his party's goals of usurping the regime. Suddenly, the 600,000 demon army mobilises to their position and they are greeted with a first batch of Corrupterment decides. As they were outnumbered, a group of Prinnies appear to their aid and declare that Valvatorez has the support of all Low, Mid and High Level Demons to help fight the Corrupterment forces.
The Hades Party fights multiple well known groups of the Corruptermen such as the Three Brutes, the Four Devas, the Seven Yakshas and the Ten Overlords. Finally, they arrive at the President's Office where they are greeted by President Hugo. Hugo asks Valvatorez why is he leading the rebel forces and Valvatorez states that it is due the demons neglecting their responsibilities. Each party member is also asked on their goal and with all them having different goals, Hugo mocks them saying how could they defeat him if they are not completely united. Valvatorez declares that it is their camaraderie that unites them and they fight Hugo. After they win, Valvatorez expects Hugo to transform into his other forms but Hugo admits that was all the power he had left. Hugo also reveals that there is little Fear Energy left in the Netherworld, being the reason why so many demons have lost their powers. It is also revealed that humans have continuously lost their fears against demons and despite the demons trying everything they could, the humans eventually overwhelmed them with their scientific technology.
A group of humans also came to the Netherworld to retrieve demon bodies in exchange for Fear Energy but they have only let little leak in to the Netherworld. The defeated President Hugo confesses that a single human has been control of the Netherworld the entire time, shocking Valvatorez greatly.
The Human World leader, Judge Nemo is revealed to have been the mastermind behind the game's events. Nemo states his purpose as a judge to humanity, stating that every human's existance is a sin. He offers Valvatorez to join him to bring Hades to the worlds and destroy them. He refuses and decides to challenge Nemo with him accepting his challenge and telling them to come to the Human World. Before they depart, they must decide on a new President which Axel shows up and takes the position as Valvatorez says there are other things to worry about. The Human World is revealed to be a place filled with scientific technology and pollution. The Hades Party is greeted by a group of Bio-Suits which Fuka recognizes them created by her dad. Nemo appears to them and reveals that the humans have made demon clones due a deal he made with President for obtaining demon specimens.
As they progress through the human factory, Fuka sees her father, Genjuro, who recognizes Desco but not Fuka. Genjuro reveals that Fuka had really died and thought see had gone to Hell due to her plans of World Domination. Once again, Nemo appears and reveals that he had been funding Genjuro's research and decides to unveil the main event, the "True Final Weapon" who had sent both Fuka and Desco to Hades, Des X. She claims it is impossible for them to defeat her but the party decides to lend their support to Fuka and Desco. Afterwards, Des X refuses to give up and reveals she had killed Fuka for stealing her dad's attention from her. Des X transforms and Fuka being angered by this, powers up and unleashes her true power. Des X is defeated again and Fuka states that her father was selfish for being so absorbed into his research. Desco reveals that the demon clones and Des X and herself were all created for Fuka. She is still angry at her dad when Nemo appears and despite Des X being defeated, states he will blow up the moon next.
Nemo escapes, and the party decides to go to the moon through the Dimension Gate. Fenrich is angered that Nemo would target the moon due to the moon being a symbol of loyality to Valvatorez. On the moon's surface, they encounter aliens who are very formal and business like. They also find out that in order to stop the destruction of the moon, they must destroy ignition devices first. Nemo appears after they destroy the first ignition device and tells them that the Pan-Galactic Alliance(which consists of 20 billion planets) had ordered the extermination of the humans on Earth. Valvatorez is still confident in stopping the destruction of the moon as he promised earlier to protect the moon and the Earth. After they destroy the second ignition device, Nemo tells them that they must stop the alien base's reactor core if they want to stop the moon's destruction. After the reactor core's destruction, Nemo tells them that the moon will fall on to the Earth because of the reactor core's destruction.
The party is dismayed and struggles to find a way to prevent the moon from falling. Suddenly, Archangel Flonne appears on the moon, telling the party that she has the solution to their problems. She also accidentally reveals that Vulcanus is actually Artina all along. Artina is shocked as she learns that all of the money she was collecting was being used to build Great Flonzor X, a robot being used to hold the moon. Flonne tells the party that Great Flonzor X needs more awe energy to return the moon to its original place. Fenrich opts for a different solution by finding the remaining aliens and asking them for an alternate way to stop the moon from falling. After defeating the remaining aliens, the party decides the only way to stop the moon from falling is to create more awe energy for Great Flonzor X. As a result, not only the entire party prays to Great Flonzor X, but all of the Demons of the Netherworld and Humans pray due to the efforts of the newly elected President Axel and Genjuro. They managed to convince their people to lend their support to the party by praying to Great Flonzor X. The moon is returned back to its original place and as the party celebrates, Nemo appears once again. He tells them that he will not stop before being consumed by dark energy.
The party notices a malicious aura in the area and surrounding the Earth. Flonne figures out that Fear the Great has been activated. Back in Hades, she explains that Fear the Great is an emergency system created by God to destroy a planet if there is too much malice. The party declares that they will stop Fear the Great and save the Earth. Flonne opens up a gate to Fear the Great for the party. The party travels to Fear the Great where they encounter beings of Malice which uses Nemo's voice. They figure out that Nemo is being possessed by Fear the Great as it possesses the human with the most malice. Fenrich notices how the malice beings speak about Nemo's family and Artina being taken away from Nemo. He demands that Artina should tell them of her past with Nemo. She explains that Nemo was a wounded soldier who wandered into her treatment clinic during a war. Nemo was previously tortured by her country and managed to escape. As a result, his country thought he was a spy and took away his family. As Nemo was an enemy of Artina's country, she was killed after being suspected of being a spy. Nemo grew more and more hateful of the human race until he deemed that Demons and Angels were responsible too for letting the humans create chaos.
Back in the present, Fenrich figures out that if they get Nemo to believe that Artina is alive, he will stop his rampage. After two failed attempts, Valvatorez convinces Nemo that Artina is here with them. Nemo finally sees Artina, and he thinks that he is a fool for doing what he did in the past. He decides to disappear with Fear the Great to limbo, where he can never reincarnate. Artina thinks that Nemo should still pay for his sins and Valvatorez decides to turn him into a Prinny. They travel to the center of Fear the Great where Nemo asks them why are they still here. They convince him that he will be able to reincarnate as a Prinny and pay for his sins. However, the core of Fear the Great possesses him and the party fights him in the final battle. After Nemo is released from Fear the Great, Nemo thanks them for what they have done. Emizel reaps Nemo's soul afterward. The narrator states that the names of the 6 members of the party were written down in history for saving the world. The credits roll afterward.