King overpowers and single-handedly defeats Guila using his Sacred Treasure, the Spirit Spear Chastiefol. As Meliodas, Elizabeth, Hawk, Diane, Ban and King return to the village, King tells the others that the Sacred Treasures of the Seven Deadly Sins unlocks each of their full potential in combat. However, Meliodas sold his, Diane lost hers and Ban got his stolen. Meliodas, Ban and King head to the Merchant Town Vaizel during the annual fighting festival, in which the grand prize happens to be Diane's Sacred Treasure, the War Hammer Gideon. Meanwhile, Great Holy Knight Hendrickson summons Jericho and Twigo underground, offering them blood from the corpse of a red demon as a means of enhancing their strength. Twigo explodes after drinking the blood, but Jericho manages to survive the excruciating experience.

Meliodas and Ban engage in a fierce fight that shakes the ground beneath them, equally matched due to their incredible strength and agility. However, Meliodas grabs onto Ban's wrist and blasts him out of the ring, thereby winning the round. The first round of the semifinals is Diane versus Howzer, in which Howzer goes all out with his windy punches, but Diane does a body slam on Howzer and wins the round. The second round is Cain versus Meliodas, in which Cain believes that Meliodas betrayed the kingdom in the past. When Meliodas says that he did not betray the kingdom, Cain trusts Meliodas and forfeits the round. The round of the finals is Diane versus Meliodas, while Guila and Jericho are making their way towards Vaizel.

Guila and Jericho interrupt the tournament and cause terror upon the merchant town. King subdues Guila and Jericho after Meliodas and Ban are defeated by them, but King is later overwhelmed by Holy Knight Helbram, who was disguised as tournament referee Love Helm. Meanwhile, Elizabeth returns to her normal size and stumbles upon her elder sister Veronica Liones, who scolds Elizabeth for being involved with Meliodas. Veronica then traps Meliodas inside Goddess Amber, a stone specifically made to seal demonic beings. Elizabeth runs away with Meliodas's sword and Goddess Amber, while Griamore temporarily restrains Guila and Jericho. Veronica catches up to Elizabeth and shields her from an explosion made by Guila, which causes Veronica to pass away. When Elizabeth calls out for Meliodas, he emerges from within Goddess Amber with a darker side to him.

With his true power finally shown, Meliodas clashes with Helbram, who takes note on how Meliodas hones his dark abilities. After managing to defeat Meliodas, Helbram steals Meliodas's sword. Ban takes Elizabeth, Hawk and King to safety, while Diane returns to her normal size and wields Gideon with attacks that crumble the earth, forcing Helbram to retreat with Guila and Jericho in tow. Elizabeth embraces Meliodas after he is rescued by Diane, later lamenting the death of Veronica. Ban and King express their motives behind taking back the kingdom. With his sword now stolen, Meliodas vows to end the ongoing war once and for all.

Gowther is welcomed by the others into their group, but he soon finds out the true secrets behind them by delving deep into their memories and emotions. Meanwhile, Hendrickson and Helbram have the hilt of Meliodas's sword in possession, in which they plan to use it as a fragment of a ritual relic, known as the Coffin of Eternal Darkness, to resurrect the red demon race as a means to start a holy war. At the Boar Hat, Holy Knight Vivian suddenly appears and kidnaps Elizabeth and Hawk. Diane throws Meliodas, Ban and Gowther toward the Kingdom of Liones, where the three are bombarded by an army of Holy Knights on the north side of the castle. However, Arthur Pendragon, the young king of Camelot, has approached the south side of the castle with his own army.

Hendrickson tries to convince Arthur to leave the castle, but to no avail. Instead, Hendrickson escorts Arthur inside the castle and suddenly engages him in battle. Meanwhile, Elizabeth and Hawk are teleported inside the dungeon of the castle, and they try to find a way out. Meliodas, Ban and Gowther manage to defeat the army and sneak inside a town of the kingdom, while King summons his black hound Oslow to use its mouth to teleport Diane inside the castle. However, Diane is attacked by Guila, Jericho, Gilthunder, Howzer, Helbram and Great Holy Knight Dreyfus. Diane tries to defend herself, but Dreyfus overpowers her with an attack that sends her crashing onto the town streets. After Diane wander the streets and protects Zeal from being crushed by a falling building, both Howzer and Guila switch sides to defend Diane.

The combined powers of Howzer and Guila have little to no effect. When Dreyfus attacks Guila, Gowther saves Guila in the nick of time and faces Dreyfus alone. Meanwhile, Elizabeth and Hawk encounter Margaret Liones, Elizabeth's eldest sister, in a cell. Vivian appears, teleporting Hawk elsewhere, knocking Elizabeth unconscious and releasing Margaret from her cell. Gowther traps Dreyfus in a nightmare, but Dreyfus somehow snaps out of it and pierces Gowther in the chest. Once a heavily injured Dreyfus leaves with Gilthunder, Helbram attempts to finish Diane off, but King appears and stops Helbram, who reveals himself as a fairy and King's former best friend. Helbram uses his magical tree roots to restrain King and inflict brutal lashes on Diane. However, King uses Chastifol to shield Diane from getting hurt. King says that he is fulfilling a promise that he made seven hundred years ago.

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 leaves Dreyfus to fight Meliodas alone, while Hendrickson deals with Arthur and ultimately defeats him. Meanwhile, Elizabeth wakes up in a chamber and finds her father, King Bartra Liones. Meliodas then finds himself outmatched against Gilthunder, Hendrickson and Vivian. At the same time, Margaret decides to take her own life by jumping off a castle tower. Margaret and Gilthunder are both released from their curse in the form of monsters, thanks to Meliodas. While Margaret is thus saved from falling, Hendrickson tries to finish Meliodas off, but Gilthunder stands in the way and knocks down Hendrickson at full force. Vivian tries to trap Meliodas, Gilthunder, Margaret and Arthur in illusionary places, but Merlin, the Boar's Sin of Gluttony, makes her first appearance and breaks the spell.

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.

Hendrickson unveils the source of his power, the corpse of a red demon, which is the same one that Ban slayed in the Fairy King's Forest long ago. After Ban pummels Hendrickson through the ground, Meliodas, Ban, King and Gowther jump down the hole to a cave, where Hendrickson injects himself with the blood from the corpse of a gray demon to acquire even more power. A sudden burst of energy from Hendrickson sends the four of them back above ground, where Hendrickson easily overpowers all of his opponents despite all of their efforts. With Meliodas left standing and protecting Elizabeth, Hendrickson casts a large dark blast, but Hawk sacrifices himself in order to save the two of them. Shocked of losing her dear friend, Elizabeth awakens her dormant powers that repels Hendrickson and heals everyone else. However, Hendrickson survives and still has strength left in him to fight.

The Seven Deadly Sins and the Holy Knights all combine forces in an attempt to defeat Hendrickson. Meliodas, given support from his friends and allies, uses his ultimate technique to finish Hendrickson off. When Bartra appears with Merlin, he commands the Holy Knights to restore the kingdom and preserve its people as their "punishment" for starting a holy war. Bartra then thanks the Seven Deadly Sins for saving the kingdom and protecting Elizabeth. Hawk is revived as a piglet, much to a surprise. Things return to normal inside the kingdom, and a festival is held at night. The next day, Elizabeth joins Meliodas, Hawk, Diane, Ban, King, Gowther and Merlin in finding the last member of the Seven Deadly Sins, Escanor, the Lion's Sin of Pride.

King is overjoyed to spend the day of the festival with Diane, but he's struggling to figure out how to take the next step.

Business at the Boar Hat is dropping, so Meliodas asks Merlin to join the staff as a waitress alongside Elizabeth and Diane to attract customers.

As the kingdom begins to rebuild after the coup attempt, the king honors the Seven Deadly Sins for their bravery with a medal ceremony.

With Fraudrin's manipulation of Hendrickson, the Ten Commandments return to the physical realm. King follows Ban to the Fairy King's Forest.

Diane confronts Gowther after he manipulates Guila and Zeal's memories. With the return of the Demon Clan, new threats descend upon allied clans.

King struggles to fend off the giant Albion sent to destroy the Fairy King's Forest. Galand of the Ten Commandments appears before Meliodas.

The fairies reconcile their differences with King as Ban leaves the forest. Meanwhile, Meliodas and gang are overwhelmed by the sheer power of Galand.

Hendrickson, thought to have been defeated against Meliodas, aids Gilthunder and the Holy Knights against a powerful Gray Demon.