Cain is an elderly man who was first introduced in Byzel's annual fighting festival as the one who led the Seven Deadly Sins to it and as a contestant. While he doesn't look like it, he is actually a former Holy Knight of Danafor.
Badass Grandpa: He might seem like a weak old man with a bad back but he's actually very strong.
Drunken Master: When he is first introduced, Cain is presented as a drunk. Despite this, he is rather skilled.
Forgotten Friend, New Foe: When Cain realizes that the person he assumed was Meliodas' son with Strong Family Resemblance was actually Meliodas himself, he presented himself as this trope. In reality though, Meliodas couldn't remember him because Cain always wore full body armor and always went by his Red Baron moniker in the past. The two also fortunately make up in the end.
Only Known by Their Nickname: He went by "The Flame Barzad" so much in the past that Meliodas never actually knew him other than that prior to their reunion.
Red Baron: In the past, he called himself "The Flame Barzad" in association to his fire abilities.
24-Hour Armor: He wore his full body armor so much in the past that Meliodas had actually never seen him out of it prior to their reunion.
A young woman who resembles Elizabeth, and who was once Meliodas' lover when he served Danafor. She was originally a slave of an enemy kingdom of Danafor before being freed by Meliodas. Initially hostile to Meliodas and the Holy Knights of Danafor, she later opened up to them.
Defrosting Ice Queen: Initially, she was rather hostile to Meliodas due to them being originally on different sides. However, she later warmed up to him and others.
Elaine is King's sister, and the Guardian Saint of the Fountain of Youth, who was killed by a demon from the Demon Clan in the Fairy King's Forest, and resides in the Capital of the Dead since her death.
Advertised Extra: Though she has so far only appeared in-story when the Sins went to the Capital of Dead and in Ban's backstory, Elaine is often featured alongside the main cast on covers as if she is a regular, usually by Ban's side.
Our Fairies Are Different: Elaine, like her brother King, was a long living child-like wingless humanoid capable of levitating herself and other things. For some reason though, only she and her brother appear to be wingless. Other fairies so far have wings.
Really 700 Years Old: She's a fairy with a child-like body but is actually over seven hundred years old when she met Ban. Due to the child-like form Elaine has, a creepy trope comes to mind when her relationship with Ban is seen out of context.
Restored My Faith In Humanity: During her time protecting the fountain, Elaine develops hatred towards humans, due to all of them trying to steal the fountain and destroy the forest, but her thoughts change when she meets Ban.
Samaritan Relationship Starter: She became interested in Ban after she told him that if he were to take the elixir, the forest surrounding it would die and Ban promptly decided that it wasn't worth it.
Star-Crossed Lovers: With Ban. She's dead and Ban's immortal however Ban is trying to find a way to rectify this.
Token Mini-Moe: Of all the female characters so far, she is the most child-like in appearance.
Multi-Armed and Dangerous: Originally started out as a two armed abomination whose fingers were arms complete with their own fingers. Later, its two main arms split into four smaller ones, thus becoming a four armed monster.
Multiple Head Case: Apart from its normal looking human head, it had several. One that was chopped off and given to Dawn Roar, and four that grew out of his main monstrous body. These later merged together to form a single multi-faced head.
The newly appointed king of Camelot who was very briefly mentioned in gossip early in the manga. Like his namesake, he pulled a sword out of a stone and became Camelot's king. He comes to Liones with a cloaked figure that is somehow able to produce a large army. His intention is apparently to visit the king of Liones, not knowing that the kingdom had been ursurped by its Holy Knights.
A Child Shall Lead Them: Like his namesake, he became king at a very young age after he pulled the sword out of the stone. He is visibly one of the younger characters of the series.
Badass: First foreshadowed by his extremely powerful presence felt amidst his huge army alongside a cloaked figure, Arthur proves himself to be this when he fights off evenly against the Great Holy Knight Hendricksen. What's more this particular battle was Arthur's first real fight against an opponent. He only staggered abit later on only on account of Hendricksen deciding to use forbidden abilities, and that Arthur lacked sufficient experience.
It's then further revealed that while Arthur has incredible latent power within him as sensed by others, he has yet to figure out what exactly his power is or how to even use it. So in other words, he was pretty much a Badass Normal when he fought against Hendricksen.
Chekhov's Gunman: He was mentioned as early as Chapter 3 of the manga as very easy to miss gossip among the drinking patrons of the Boar Hat. 59 chapters later, he comes to Liones in full force.
Comically Missing the Point: When he met King Bartra Liones in his youth, Arthur was told that instead of becoming a Holy Knight as he had always dreamed to become, he would become something much greater, a king. From this momentous prediction, all that Arthur took from it was that he was never going to be a Holy Knight.
Cool Helmet: He wears a vaguely demonic looking helmet.
Cool Sword: He apparently possesses two swords, each with a different intricately designed hilts. One that he pulled out of the stone, and one with crosses that act as the ends of its cross guard and its pommel.
Didn't See That Coming: The Holy Knights and the Sins were so busy with their own affairs that they didn't see Arthur and his entire army coming.
Fights Like a Normal: Arthur was forced to fight against Hendricksen without the aid of his own power due to him not yet knowing what type of power exactly he has. He proves to be a match for the Great Holy Knight in regular combat.
How Do I Shot Web?: Based on what others sensed from him, Arthur has incredible latent power. The only problem is that he doesn't even know what type of power he has. Still without even knowing what type of power he has, Arthur was able to hold his own against a Great Holy Knight.
Idiot Hero / Idiot Savant: Idiot can best describe certain aspects of Arthur such as him not knowing what type of power he has despite it being incredibly strong. Regardless he proves to be incredibly heroic and proficient in regular combat.
Hauser: Is this guy... an idiot?
Guila: Either that, or he really is something...
Idiot Hair: Arthur has a long part of his hair which sticks out prominently in a rather distinctive shape.
The Pollyanna: As shown in a special side chapter depicting Arthur meeting King Bartra Liones as a child, Arthur generally had an upbeat and rather hopeful attitude. Best demonstrated when he was saved from his adopted brother Kay's attempt to seriously injure Arthur by Bartra, all that Arthur did was calmly thank Bartra immediately rather than react to terror to the severity of the situation. Arthur even easily forgives Kay citing that one day they maybe the best of friends.