The "Seven Deadly Sins," a group of evil knights who conspired to overthrow the kingdom of Britannia, were said to have been eradicated by the Holy Knights, although some claim that they still live. Ten years later, the Holy Knights have staged a coup d'état and assassinated the king, becoming the new, tyrannical rulers of the kingdom. Elizabeth, the king's third daughter, sets out on a journey to find the "Seven Deadly Sins," and to enlist their help in taking back the kingdom.
The third princess of the Kingdom of Liones, Elizabeth, finds Meliodas, who is the owner of the Boar Hat bar and is also one of the Seven Deadly Sins. With her identity exposed, she is pursued by Twigo whom Meliodas quickly defeats. The princess joins him on his journey to find the other Deadly Sins in order to defeat the Holy Knights, who have orchestrated a coup d'état and have overthrown the king.
Gilthunder, thus preventing the village from making the Bernia ale, which was their prime source of income. After innumerable unsuccessful attempts of the villagers to remove the sword with which the source was blocked, Meliodas easily removes the object. A celebration is held at the Boar Hat, and Meliodas was hailed as a savior by Bernia's villagers. Gilthunder, wanting to confirm whether the removal of his sword was an accident, threw a spear imbued with his power toward the town. Meliodas, however, easily stops and throws the spear back, destroying Fort Solgales.
Meliodas, Hawk and Elizabeth travel to the Forest of White Dreams that even Holy Knights avoid. There, the Prankster Imps that inhabit the Forest of White Dreams attempt to confuse them by impersonating Hawk and Elizabeth in order to lead them away. After defeating them, they follow them and find the Serpent's Sin of Envy, Diane sleeping in the forest. Gilthunder suddenly arrives and binds all of them with his lightning magic. Meliodas battles Gilthunder, purposely allows the Holy Knight to slash him, and under the pretense of dying due to the grave wound, acquires information about the whereabouts of two members of the Seven Deadly Sins, King and Ban, as his apparent last wish.
Having discovered the whereabouts of Ban and King, Diane throws Gilthunder out of the forest, and Meliodas, Hawk and Elizabeth, now joined by Diane, head toward the Baste Dungeon, where Ban is imprisoned. They later arrive at Dalmary Town where Meliodas is treated by Dana. Diane and Elizabeth begin to argue and discuss about the aspects in which they envy each other. They are suddenly attacked by the Holy Knight Friesia, who tries to destroy the entire town along with the Deadly Sins, but Diane quickly destroys all of her insects. Concurrently, Ban escapes from his cell in the Baste Dungeon, and is stopped by Jericho, who tries to subdue him. Dana unexpectedly reveals that the medicine Meliodas drank was a deadly poison as Golgius appears out of the blue.
Golgius appears and attempts to take Elizabeth and Meliodas' sword back to Liones. Whilst attempting to take the sword, Meliodas awakens, with no effect of the poison showing, proceeding to blast an aura that causes Golgius to make a hasty retreat. Meliodas and Elizabeth set off to Baste Dungeon afterwards, however, they are stopped by a confused Diane, who after hearing the sound of a bell, attacks the group. They try to run away from the berserk Diane, involving a pair of shepherds along the way, however Meliodas soon succumbs to the same bell, and begins to fight Diane. Meanwhile in Baste Dungeon, Ban is shown wandering around after having dealt with Jericho. It is not long before he is found by Jude of the Weird Fangs, who promptly stabs Ban in the chest.
Meliodas and Diane are still fighting each other; Elizabeth shouts for them to snap out of it, and for a few moments they do, until the sound of the bell once again spurs them to fight each other again. The Holy Knight Friesia comes in, threatening the life of the shepherds, however Elizabeth steps in to protect one of them, heavily injuring herself in the process. It is then revealed that one of the young shepherds is actually Ruin, and that he has been fooling them all this time. As Elizabeth gets beaten up by Ruin, she manages to knock off the bell that is causing the hallucinations; Ruin goes to punish Elizabeth further for doing so, but Meliodas quickly comes to her aid, thus beginning Meliodas' battle with Ruin, whilst Diane faces off against Friesia. Both defeat their respective opponents, and the team continues their trek to Baste Dungeon. Elsewhere, despite having been pierced in the chest, Ban is able to overpower Jude, and takes him out. Meliodas and co. finally enter Baste Dungeon, although it is all a trap as Golgius locks them in with the Eternal Seal Spell. However, the reunion between Ban and Meliodas caused so much destruction that it completely destroyed the structure and disregarded the spell. Later that evening, the gang enjoys a meal courtesy of Dana, but an omen in the sky foretells of great disaster to befall Britannia soon. In Liones, it is revealed that King is alive and well, but he is working with Gilthunder.
Meliodas picks the ggroup's next destination to be the rumored location of the King, the Capital of the Dead.
King has a final confrontation with Ban, finishing him off with Ban being frozen, with Elaine making an appearance, never showing herself to King. A holy knight Guila battles it out against Meliodas, Diane and Elizabeth. Ban continues his flashbacks with Elaine and the Fairy forest, at the foutain of youth.
The battle with the King comes to a close as he overpowers Guila with Chastiefol. Their time in the Capital of the Dead now over, Ban and Elaine have one more close moment, before being bid a farewell by Ellen and Luigi, who are revealed to have been ghosts this entire time...
The Byzel fighting festival commences! After the initial brawl only leaves 8 people standing. The three first rounds unravel with some interesting displays of power and a few surprises.
It's Meriodas vs. Ban in a a fight that shakes the ground beneath their feet. The semifinal rounds end up with the sins gaining one new friend and remembering an old one. Everything is ready for the final match while a storm starts brewing in the horizon.
The final round draws to a close. The Holy Knights descend upon the sins giving them some new powers and improved equipment. The Deadly Sins are pushed against the ropes.
Meliodas is freed and the power of the Captain sin makes its debut. Possessed by a strange darkness, Meliodas assaults both enemies and allies until he clashes against Hellbram, the two of them fight mercilessly.
News of an armored giant walking around the mountains reach the holy knights and they quickly send an assassination squad to deal with it. In the meantime, Meliodas's group also finds out about the mysterious giant. The holy knight team, the sins, and the giant clash in three-way battle with a very interesting outcome…
The sins confront a strange demonic being. Meliodas is about to deal the final blow when he loses heart and stops attacking. In the meantime, Elisabeth discovers some facts about Meliodas's past. In the end, Elizabeth rushes to the battleground and her words give Meliodas the courage to fight to his full potential. When the sins inspect the dead body of the monster they find out it was some kind of hybrid between human and demon.
Hendriksen and Hellbram make their first attempt to bring back the demon clan using the handle of Meliodas's sword, but the experiment fails and they appear to be missing one ingredient. Far away from there, Meliodas's group is taking a break from all the fighting…
Hendriksen and some of his guards welcome Arthur and his companion, a short person covered with a cloak. Meanwhile King finds a way to transport Diane and him to the city of Liones.
After a fight starts, Howzer and Guila combine their powers to protect Diane and Guila's little brother from the combined forces of Githunder, Helbram, Dreyfus, and Jericho.
The King reminisces over some old memories of a time Diane and King spent together when Diane was still a giant child. Back to the present, King fights Hellbram, while in a different location Hendriksen fights Arthur.
Gilthunder arrives to support Hendriksen against Meliodas, Arthur tries to keep Hendriksen busy while Meliodas fights Gilthunder, but has to withdraw leading to a three way fight...
Ban explores the catacombs under the city. Merlin and the other sins go to the chamber where the king Baltra and Elizabeth are being held captive. Dreyfus has a confession.
Ban attempts to kill Meliodas, but is stopped by Hawk. Meliodas and the sins corner Hendriksen and prepare to take him down.
Hendriksen turns into an incredibly powerful monster. As Hendriksen overpowers both the sins and the holy knights only Meliodas is still standing...
After the defeat of demonized Hendrickson, The Seven Deadly Sins are commended for their bravery and courage by King Bartra. However, just before the ceremony, Ban and King leave. Earlier, Ban had told Meliodas that he is quitting the Seven Deadly Sins. As Ban leaves the Boar Hat Bar, King sees him and asks where he is going. Ban tells King that he wants to go to the Fairy King Forest. King then accompanies Ban on his journey. Meanwhile, it is reveals that Hendrickson has survived the assault from the Sins and he is shocked upon seeing Dreyfus alive. Dreyfus then summons the Commandments, ten demonized warriors who intend to destroy the Sins.
The Ten Commandments are in the process of recovering their magical powers and fly to the Kingdom of Edinburgh in the east. Meanwhile, Jericho is discovered following Ban and King on the journey to the Fairy King's Forest. In the forest, the fairy people call King a traitor because he left the Fairy King's Forest 700 years ago, his absence allowing the forest to be almost entirely destroyed, while Ban is called the new Fairy King because he planted the last Sacred Tree seed that Elaine entrusted to him. Diane and Elizabeth admit to each other their love for King and Meliodas respectively. Meanwhile Gowther, believing he needs to experience love, alters Guila's memories so she forgets Zeal is her brother and thinks Gowther is her boyfriend, while Zeal, who Gowther considers a barrier between himself and Guila, loses his entire memory. Gowthers manipulation of their memory enrages Diane and she attacks him without hesitation.
Diane defeats Gowther. The Ten Commandments discover the remains of a magical explosion and conclude it was caused by Meliodas. Gowther restores Guila’s memories. Merlin temporarily returns Gowther to his original form, a 6 inch tall wooden doll, and gives him to Slader for safekeeping. Sensing a magical disturbance Merlin transports the Boar Hat to Camelot which is being attacked by a giant Golem which Meliodas recognises as Albion, a magical weapon created by the Demon Clan, which awoke after it sensed the return of the Commandments. Meliodas breaks the sword he received from Liz so Merlin gives him back his sacred treasure, the sword Lostvayne, which she had retrieved from the pawn shop he sold it to. With Lostvayne returned Meliodas destroys the golem instantly. In the Fairy Kings Forest King and Jericho are surprised when the trees begin growing rapidly, which they realise is due to Ban feeding the forest with his blood which contains water from the Fountain of Youth, something the other fairies reveal he does every few years in honour of Elaine’s memory. The forest is suddenly attacked by another Albion Golem.
As the Golem begins destroying the forest King battles to protect the new Sacred Tree. Gerheade, the traditional servant of all past fairy kings, refuses to acknowledge Ban as king of the Fairies. She is surprised when Ban agrees with her, as he never wanted to be king. But, rather than let him leave the forest, she attacks him, knowing that he would risk himself to protect Elaine’s body and traps him, intending to use him as the new Fountain of Youth. King fails to stop the Golem and is injured while the Sacred Tree is destroyed for a second time. Gerheade prevents King from attacking the Golem while the other fairies rush to fight it, sacrificing themselves so King can escape, for as long as King is alive the forest will always grow again. King, however, refuses to flee, gaining strength from his desire to protect the forest, fairies, and even Ban he succeeds in transforming Chastiefol into its True Spirit Spear form and destroys the Golem. Back in Camelot as they recover from destroying the Golem they are attacked by Galand, one of the Ten Commandments, who is at least several times stronger than Meliodas.