A tired and thirsty Furuichi finds himself in a desert, accompanied by Oga, Baby Beel and Kunieda. Furuichi asks what the hell is happening but Oga replies that this is Journey to the West, that he is the monk Sanzohoshi and they are traveling to Tenjiku (India) to retrieve the Buddhist Scrolls. Before dusk, Oga and company arrive at a village populated by people who look like Shiroyama. The townspeople prepared dinner for the four of them. They continued their journey, with more and more people accompanying them along the way, first the Six Holy Knights, then the Red Tails, then the MK5, until the whole of Ishiyama accompanied them to the doors of the Ox King's castle. They were surprised, however, to find Lord En and his three maidservants inside. En tries to hold a New Year's party for his newfound "friends" (Isabella comments that En does not have friends who visit him at New Year) by playing a card game. However, Furuichi beats En at the game, causing the latter to cry and set the Ox King's palace on fire. They later find out that the Ox King is not the Demon Lord himself, but Tojo, and he steals all of the octopuses from the village in order to make Takoyaki, as it was his part-time job. Oga borrows Tojo's fan and tries to quell the flames, but to no effect until Tojo comes with the real Bassho Fan and extinguishes the flame. After chiding En being a pain in the ass, Tojo invites everyone present to a Takoyaki party, at which point Oga and Baby Beel forgets totally forgets about their quest and joins in eating.

The festival is underway, and Azusa is trying to run a Maid café. Furuicihi offers to help, and Azusa and her friends obey his commands blindly due to his reputation as 'The Strategist'. Furuichi persuades many of the Red Tails to dress up in Maid uniforms, claiming that this is a preliminary battle against a café that the 6 Holy Knights are running elsewhere. Hilda also gets involved, and remodels the café to be more formal. Some rowdy guests from Teimo High enter the cafe acting unruly, whom Hilda is quick to discipline.

Tatsumi Oga, a delinquent student at the worst high school in Japan, arrives at school with a small baby who emits massive shocks of electricity whenever it cries. Oga claims he found after splitting open a strange man who came floating along the river, though his friend Takayuki Furuichi doesn't quite believe. Whilst at Takayuki's house, they are both approached by a demon woman named Hildegarde who claims the baby, known as Kaiser de Emperana Beelzebub IV, is the son of Devil King who was sent to Earth to find a human to raise him so he could destroy humanity.

Beelzebub has been crying all night for the past three nights, which is causing Oga and the whole neighborhood to get very little sleep. Wanting to stop his night crying to avoid being chased out of their house, the Oga family attempt to play with Beelzebub all day in order to tire him out come nighttime. Despite managing to get him to sleep, Beelzebub still wakes up and cries in the middle of the night. After Oga spends the day dealing with a sleep deprived Tōhōshinki, Hilda brings a toy that calms Beelzebub down, but is even noisier than his crying.

Takayuki is dragged away from his tropical summer vacation against his will to join Oga and Beelzebub to a public pool, though Oga is soon shocked by the fact he could've gone to the tropical resort himself. Whilst chatting with the Red Tails, Takayuki is approached by some delinquents from his old middle school and ends up going against their leader, Takashima, when they start hitting on the girls. Takayuki tries to hide in the pool, but Takashima calls more of his men and tricks the lifeguard into evacuating the pool, leaving Takayuki and a stunned Oga. As Takayuki becomes surrounded, he forces Beelzebub to cry in order to shock all the delinquents before facing Oga's wrath.

The students of Ishiyama High are ordered to do physical examinations amongst themselves. Baby Beel gets jealous of a toy which accidentally gets stuck to Oga's back, and locks himself inside of a locker to pout in protest. While trying to lure him out, the girls come into the room for their physicals, forcing Oga and Furuichi to hide under the desk while the girls strip off and start measuring. The girls leave the room without seeing them, despite a few close calls, and upon the girls' departure Oga and Furuichi get up from under the table and start trying to lure Baby Beel out once more. Aoi returns to the classroom moments after leaving, and finds the two of them in the room. She realizes that they have been there all along, and goes on the offensive. During the conflict Baby Beel exits the classroom through an open window and climbs into Sadohara's sports car, and locks the door behind him, which Oga is unable to pull open. Baby Beel "springs a leak", filling the car. Oga, unable to think of any other option, chops the car resulting in the entire shell of the car shattering.

Beelzebub is currently in a phase of non-stop urination that threatens to flood the city. Hildegarde manages to temporarily stop it with an interdimensional diaper, but in order to stop it completely, Oga decides he needs to get a super absorbent daiper advertised on telly. Upon reaching the supermarket only to find the brand had already sold out, it is taking hostage by a group of thugs. As Oga probes everyone to see how ruthless they are, Beelzebub's diaper gets stuck on the leader's gun. Whilst the leader considers raising Beelzebub, Oga ends up changing his mind and beats him, before they decide to hover Beelzebub over the ocean to finish urinating.

Oga begins his training with Ittousai while Furuichi and Lamia enlists the help of their Ishiyama classmates to search for Lord En. Can Oga and Beel complete their training in time and will Furuichi and Lamia find Lord En before he destroys the city with his army?

Furuichi's group go to Himekawa's home, to start searching for En in online games. When they arrive they find the place is a giant skyscraper building, with several rooms dedicated to gaming. Most of the group have never played games, except for Chiaki, who immediately proceeds to find En in an online fighting game. Furuichi tries to get him to tell them where he is, and when he finally answers he tells them they have to beat him in a game before he tells them. Tatsumi tries to escape from Saotome, but is unable to throw his teacher off, even after showing off his new rock splitting abilities. It isn't until later in the episode that Beel takes matters into his own hands and decides to let Saotome train him. With Saotome training Tatsumi, the group's first teacher substitues for them, but everyone is away doing their own thing, except for the girl with the face mask, who for some reason got left behind.

The episode opens with a distinct sci-fi feel, before moving into the game, where the Ishiyama group are in the middle of getting their asses handed to them. They are unable to do anything against the tank. Then Yuka shows up, driving a giant robot called the Crazy Frog. She crushes the tank, and proceeds to kick and tap dance all over the other vehicles. Up until she steps on a mine and loses the tank. Tatsumi's training goes more like an aerobic workout, complete with lame musical accompaniment. He complains about this, calling out for being an exercise, and not training. Meanwhile the gamers run into more trouble when En's team start using an invisibility cheat. Himekawa realizes what they are doing, and goes to prepare some countermeasures. While Tatsumi does pushups, Saotome tells him that Tojo asked to be trained, and if he isn't careful Tatsumi will be overtaken. Saotome uses a recording of Tatsumi's voice to make a training partner who has all his hidden strength.

The Demon King sends Beelzebub some summer homework, containing a notebook which brings anything drawn in it to life. Next, Hilda brings Oga to Ishiyama High to collect prints of rare, powerful beasts, aka the delinquents, by whacking them with a giant fly swatter. During the chase, Beelzebub ends up planting several carnivorous Demon Plants, one of which grows into a massive giant causing havoc until Oga destroys it.

Finding Alaindelon's daughter rather attractive, Furuichi vows to rescue her while Gare and Edda leaded him to Oga and Lamia in the village of thieves where Alaindelon's daughter, Angelica is trapped. The rescue runs smoothly until a large Demon named Vlad's Master is awakened and terrorizes the village in which Beelzebub suddenly growed bigger and larger to fight it off.

The students of Ishiyama High settle in at St. Ishiyama, with all the significant characters being placed in the same classroom. Their new homeroom teacher, Sadohara, challenges Tojo to an arm wrestle to try to establish some authority over the class, failing miserably when Tojo accidentally slams him upside-down against the wall. He then picks a second target, Oga, who was sleeping in his seat, and wakes Oga in order to challenge him. Baby Beel is angry to have been woken and subsequently tantrums, shocking Oga and Sudohara.

The show opens seeing the 2 pillars who got beaten in jail, and 2 other pillars talking to them. One is Lamia's mom. They then cut to the main gang who are tired from playing video games. Shiro acts as Lamia while talking to En. He speaks like a ditzy schoolgirl, but En buys it.

Hildegarde presents herself to Oga's family in the wrong way, giving them a different view of the situation. She also informs Oga that if he is more than 15 meters away from Beelzebub, his cries may destroy the city. Whilst dealing with this situation, Oga comes up with the idea that, if he can find someone more strong and ruthless than him, he can dump Beelzebub on him and be free.

After a sleep deprived night, Oga notices he has a strange mark on his hand, revealed to be Zebel Spell, a symbol of the contract between him and Beelzebub. Hildegarde and Alaindelon explain that a Demon Lord's parent is a vessel for his power, and the mark will grow the more opponents Oga defeats. Wanting to get rid of the mark, Oga decides to give up fighting in the hopes it'll make the mark smaller. Meanwhile, another delinquent, Tatsuya Himekawa, hires some thugs to kidnap Hildegarde and Takayuki in order to get Oga's attention. Oga uses Alaindelon to sneak in and forgoes his promise to beat Tatsuya's henchmen. Tatsuya goads Oga into hitting a cermanic plate hidden under his shirt, but his punch is so powerful it knocks him out anyway. Tatsuya then tries using a stun rod, but Oga resists it and uses Beelzebub's power to beat him, which in turn makes his mark larger.

The mark on Oga's arm goes back to its small size, much to the chagrin of Hildegarde who destroys his games console. She brings a play room for Beelzebub to play in, but upon building it, it turns out to be a magical cage that both she and Oga get stuck inside. The only way to get out is to have Beelzebub solve a block puzzle toy, but he just ends up breaking it. Frustrated, Oga utilises his Zebel power to punch his way out, though it makes his mark grow big again. Rummaging through a bag of demon world toys, Beelzebub opens a chest that transforms Oga and Takayuki into nurses, which can only be reverted by helping Beelzebub play Doctor. Oga decides to use the opportunity to try and do good deeds and get rid of his mark, though has trouble handling the demonic medical supplies. After some failed attempts at treating some of the students, they change back after discovering an actually useful tool on Beelzebub's costume, but accidentally triggers an explosive that negates all the work Oga did getting his mark down to size.

Himekawa plots revenge against Oga by setting him up with a poisoned sandwich, but it doesn't affect him due to his resilience to Hilda's cooking. He next attempts to use a popular costumed character in order to try and capture Beelzebub, but Oga and Beelzebub notice that he's a fake due to differently colored chopsticks. He later attempts to seduce Takayuki into giving him Beelzebub, but Alaindelon intervenes, transporting Himekawa and his gang to a far off island. The resulting failures leave Himekawa with no money to hire any more henchmen. Ans as he tries to attack Oga by himself, he gets caught up in fighting against a rival gang also attempting to kill Oga. Afterward, Kanzaki offers him one of his yogurt drinks, to which Himekawa repays him with a year's supply with a month long lifespan.

As Ishiyama High holds an assessment test for its studyphobic students, the Great Demon Lord also holds a test for Beelzebub, requiring him to earn points by beating up various things, or run the risk of both he and Oga facing remedial classes in the Demon World. With Beelzebub not showing much hope, Oga decides to try and dump Beelzebub on whoever scores highest on the test. When a rival school interrupts the test, Oga fights them off to allow the other students to keep on the test, earning enough points to avoid remedial lessons, later learning that the smartest student it actually Takayuki. Later, Hilda prepares a letter to the Great Demon Lord, writing reports on Oga, his family and the Tōhōshinki.

Oga reflects on Lamia telling him to take a shower before going to Tojo and sees a silhouette outside his bathroom window and thinks it's Lamia, but it's really Shiroyama, who takes Oga to Kanzaki and Himekawa who tell him they want to team up to beat Tojo and Oga agrees. On the way to Ishiyama High, they are surrounded by a large group of delinquents, which Oga takes care of swiftly. Upon arriving at Ishiyama High, the rest of the school is there to confront Oga, only to have Kunieda and the Red Tails take care of them for him. Tojo sets off fireworks in order to try and cheer up Beelzebub and all the delinquents are captivated by them. Oga confronts Tojo and Tojo is willing to give Beelzebub back only to have Oga tell him that whoever Beelzebub wants to stay with is up to him. Beelzebub's fever breaks and he immediately goes to Oga and climbs on his head, and a flashback shows Oga reconnecting the bond between him and Beelzebub. Just as the episode ends, Oga and Tojo are about to begin their fight.

In order to make up for forgetting his daughter's birthday, Alaindelon brought Angelica to Furuichi's house for a tour of the Human World. Unfortunately while the gifts were being retrieved from Alaindelon, a Yople alien teleported into the human world and escaped. Angelica resolves to track down the Yople, using a demon wand that transforms its user into a Magical Girl. Gathering 4 other girls - Hilda, Azusa, Honoka and Aoi, they form the 5 Fairies of Light and manages to track down the Yople at an amusement park where Tojo was working as part of the cast in a Gohan-kun theatre drama. A rival girl gang challenges Aoi while they were capturing the Yople and a fight ensures. Eventually, Furuichi manages to pin down the Yople and both of them are teleported away with Angelica's ability. Furuichi eventually returns back to the human world through Alaindelon, leaving him to wonder if he was even inside Angelica at all in the first place. Unfortunately, Angelica left before Furuichi could ask her about it.

The match between Ishiyama and the 6 Holy Knights is here, and this is not your usual volleyball! With their pride and their educational future on the line, the Ishiyama gang puts it all out there on the court! Will Furuichi the Strategist be their trump card?

Kiriya, the man who scarred Miki and tried to attack Oga in the past shows up at the volleyball match. He declares that he is seeking revenge on Oga, and has taken hostages at the school to stop anyone interfering. Kiriya reveals that he had to move away to Nara previously, and this is why he is only now seeking revenge on Oga. Miki, who also moved to Nara after being beaten by Oga, realizes that Oga had only beaten him to protect him from Kiriya when the two of them were both in Nara. Oga and Miki team up to take down Kiriya's henchmen while the 6 Holy Knights, the Red tails and the Tōhōshinki incapacitated all of the Keimo High students holding the St. Ishiyama students captive.

Oga attempts to explain the whole situation to Aoi, but him and Furuichi get stuck on remember BabyBeel's name. Not long after, a demon maid servent who looks similar to Hilda named Yolda appears, and expresses her unhappiness on the situation. Soon another 2 demon maid servents appear along with a young boy who is introduced by the maids as Lord En, BabyBeel's older brother, who has come due to BabyBeel taking too long to destroy humanity. Aoi then understands everyone that's going on. BabyBeel and Lord En do not have the best relationship, where BabyBeel is constantly ignoring the attention-seeking Lord En, making him upset. Lord En is also seen to love anything to do with games.

Before destroying humanity, Lord En wants to experience everything in the human world. As Lord En is a huge fan of games and the like, he is drawn to the game centres and amusement parks there and is distracted from his original mission of destroying humanity. During the visit to Ishiyama Land it's found that he cries very easily over the slightest things that BabyBeel does or happens in general. He suggests going on a roller coaster, which everyone is against due to his crying, but still he demands to go on. He does eventually end up crying and creating fire once again on the roller coaster. Lord En then alerts Oga that he may be attacked by his private guards.