You should watch the ongoing anime Nanatsu no Taizai.
It's set in Arthurian era Britannia, though Arthur hasn't conquered all of Britain yet, he has just pulled the sword from the stone, and rules over Camelot. In this universe, the various kingdoms of Britain are protect by powerful soldiers called holy knights, who wield incredible magic.
In the kingdom of Lions, there existed a group of knights known as the Seven Deadly Sins, a group of holy knights that individually possessed power beyond the powers of any other Holy Knights.
However, 10 years before the start of the story, the Seven Sins slew the leader of the holy knights of the kingdom, The Great Holy Knight Zataras, and attempted to overthrow the kingdom, but were defeated by the combined force of all the holy knights in the land, with many believing them dead, though rumors of their continued existence remained.
Now, at the start of the series, the new Great Holy Knights have lead their own coup of the kingdom, locking the King away and telling everyone he is ill, and capturing and imprisoning his daughters. Only the third princess of the kingdom, Elizabeth, managed to escape, and now seeks to find the Seven Sins, as they are the only ones with the power to defeat the holy knights, and free the king.
After spending two weeks wandering the countryside, hiding in a suit of armor, Elizabeth stumbles into a bar, murmuring of the Seven Sins, which draws the attention of the local knights, and forces the bar's owner to protect her. Much to her surprise, the seemingly young owner of this bar happens to be Meliodas, The Dragon's Sin of Wrath, the former commander of the Seven sin, who agrees to help Elizabeth save her father.
Now Meliodas and Elizabeth much travel across Britain to find the other Sins, while fighting off the holy knights that try to stop them.
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All the sins are stupidly overpowered
-The Dragon's Sin of Wrath, Meliodas, is a 3000+ year old being with super human strength and speed, and the magic ability of full counter, which allows him to reflect any magical attack back at its source with 100 fold power.
-The Serpents Sin of Envy, Diane, is a 700+ year old giant woman, over 30 feet tall, and has the power of creation, the ability to manipulate the earth summoning huge spikes from the ground, the ability to turn ground into quicksand, and the ability to lift pieces of land as large as small villages into the air and dropping them on her enemies, on top of her already massive strength. Her powers are further amplified by the 2,500 pound war-hammer Gideon.
-The Fox's Sin of Greed, Ban, is a man who drank the fountain of youth, becoming a true immortal, able to revive himself even after having his head cut off, split in half, having all of his bones crushed, etc. etc., and possesses the power of snatch, the ability to steal from his opponents, even at a distance, including his enemies strength, and speed, which he can give to himself increasing his own power.
-The Grizzly's Sin of Sloth, King, is the 1000+ year old king of all fairies, and possesses magic powers great enough to have kept entire kingdoms at bay single handedly. He also possesses he magic spear chastifoul, which he can command with his mind, and turn it into everything from a single spear, to a hail of daggers, to a massive sunflower that shoots an energy beam, and everything in-between.
-The Goat's sin of Lust, Gowther, is possibly a homunculus, which gives him the ability to change parts of his appearance at will, and he possesses the power of Invasion, which lets him enter people's minds and alter their memories at will, and can even trap people forever in their own worst nightmares. His power is enhanced by his bows of like, Herritt, which allows him to use invasion on large groups at once.
-The Boar's Sin of Gluttony, Merlin, is THE Merlin from Arthurian legend, though its a girl in this manga/anime, and she is the greatest magic user in all of Britain, and possesses the ability to teleport herself and others, and has the power of absolute cancel, which allows her to negate any magic spell she touches.
The final sin, the Lion's Sin of Pride, Escandor, hasn't shown up yet in the manga or anime, but it's believed that he is a vampire