WARNING: The following contains spoilers for Season 5 of The Seven Deadly Sins, now streaming on Netflix.
The introduction of Cusack and Chandler in The Seven Deadly Sins anime revealed the pinnacle of power within the Demon Clan. The two ancient demons were so strong, in fact, the Demon King made them responsible for training his two sons, Zeldris and Meliodas. Season 4 of the anime fully displayed this power, as Chandler was able to take on the Sins with little effort. However, Season 5 reveals that neither demon had shown their true power yet.
Episode 9 of The Seven Deadly Sins' fifth season, "That Which Gathers," changes that. After being pushed to the edge of their abilities, Chandler and Cusack suddenly transform. However, instead of evolving individually, the two ancient demons merge into the Original Demon. As he refers to himself, the Sinner was the Demon King’s first creation and the most powerful creature in the Demon Clan, aside from the Demon King. However, the Demon King separated the beast into two separate entities as punishment for attempting to overthrow him. Upon seeing the monster, Merlin says that all hope is lost.
After a few moments, Chandler and Cusack’s forms merge, and in their place stands the Original Demon. Despite being a combination of Chandler and Cusack, the Original Demon’s appearance does not resemble either of the ancient beings. Standing much taller than either of his counterparts, the Original Demon has four arms, holding both Chandler and Cusack’s weapons, and a feline-like lower body with four legs.
The battle quickly shifts as Escanor and Merlin are overwhelmed by his power. Even King’s spear Chastiefol, upgraded via King's recent power boost, is simply brushed off by the Original Demon. It is not until Ludociel rejoins the battle, this time in his original form, that the creature is forced to activate its true power, Crisis. Similar to Wild’s full-throttle ability, Crisis increases the demon’s power at the cost of his lifeforce.
As things get increasingly grim, a light parts the darkness around the battlefield, revealing Mael, who had reunited with his Grace, Sunshine. Finally able to use his Grace again, the strongest of the archangels attacks the Original Demon, once again dividing him into Chandler and Cusack.
This new form highlights the ever-increasing climbing power scale of The Seven Deadly Sins universe. As the story reaches its climax, the Sins reach the pinnacle of their own abilities as they battle some of the strongest opponents in the world.
For example, the first season of The Seven Deadly Sins revolved around the conflict between the Holy Knights of Liones, in which the power of a grey or red demon was insurmountable by almost every knight in the nation. Fast forward to Season 3 of the anime, and Sins are forced to take on the Ten Commandments, ten of the most powerful demons within the Demon Clan, leagues above the grunt red and grey demons.
Now in Season 5, the story has upped its stakes again as the Sins join forces with the most powerful warriors of the Goddess Clan to take on the upper echelon of the Demon Clan. Now that the Sins have reached the pinnacle of power, the end of their story is in sight -- or so it seems.