WARNING: The following contains spoilers for Season 5 of The Seven Deadly Sins, now streaming on Netflix.
Season 4 of The Seven Deadly Sins anime introduced Meliodas as an antagonist to the series. Following his death at the hand of the Ten Commandments and his subsequent resurrection, the former protagonist appeared much colder and more sadistic than the goofy pervert fans of the series had come to love. The season later revealed that Meliodas's new demeanor resulted from a curse placed upon him by his father, the Demon King.
The curse placed upon Meliodas was the curse of immortality. Every time Meliodas died, the Demon King's power would resurrect him. At the same time, the process would seal his emotions in Purgatory, as they got in the way of him becoming the next Demon King. To prevent this from happening, the Seven Deadly Sins sent Ban to Purgatory to free Meliodas's emotions, but as Season 5 details, the journey is no easy feat. And by the end of it, neither Ban nor Meliodas is the same.
The Hellish Conditions of Purgatory
Before sending Ban to Purgatory, Merlin described the realm in great detail to the rest of the Sins, as her father had been able to visit it. She explained that it is impossible for any living being to come back from it alive, as her father's health had been greatly diminished within mere minutes after stepping foot in Purgatory. According to her father, "the air there was mixed with the most scorching heat and blistering unbearable cold… and the earth is deadly toxic. It destroys the flesh of the living. Space-time itself is warped there so that the passing of one minute could change into that of a year."
How Ban Discovers Meliodas In Purgatory
The Seven Deadly Sins' first episode of Season 5, "From Purgatory," opens with a sizeable fox-like creature roaming through a hellscape, fighting other creatures. Suddenly, this beast begins to recall scenes from its past, seemingly causing it immense pain. After a short while, the beast transforms into a familiar face, Ban. Thanks to his immortality Ban can survive the harsh conditions physically, but after potentially centuries (in Purgatory time) of searching for Meliodas, he's on the verge of madness.
However, true to his character, Ban perseveres, eventually coming upon a dragon-like creature. After fighting for decades -- evidenced by Ban's hair-growth throughout the fight -- the beast reverts to its human appearance, Meliodas. Despite accomplishing his goal of finding Meliodas after such a long search, Ban reveals he does not know how to return to their world. As a result, Purgatory is used as the setting for most of Season 5, and its unique nature helps advance both Ban and Meliodas' arcs within the story.
Ban's Development Through Season 5 of The Seven Deadly Sins
After centuries of searching for his captain, Ban's body begins to adapt to the extreme conditions of Purgatory. In Episode 2 of Season 5, Meliodas comments on this, noting how Purgatory had drastically changed Ban's body and mind. Ban simply laughs in reply, stating that he merely hoped he'd be strong enough to go head-to-head with one of the Ten Commandments. As it turns out, Ban's development reaches far beyond the levels of the Commandments.
How Ban & Meliodas Escape Purgatory
Season 5, Episode 2, "Encounter With the Unknown," reveals that the gate to the real world is guarded by the Demon King himself, ensuring that Meliodas' emotions would never be able to escape. As he and Ban traverse Purgatory, Meliodas -- rather Meliodas' emotions, who take corporeal form -- explains that he does not possess his power because he is not the real Meliodas. This leaves Ban with the burden of being the pair's strongest combatant, the only one capable of defeating the Demon King.
The pair are guided to the Demon King by Wild, an inhabitant of Purgatory, who is searching for his lost brother. Together, the trio engages the Demon King, a being of god-like power, and fights him for over 60 years. During this time, Ban's abilities develop even further, allowing him to share his immortal life energy with others.
Eventually, thanks to Wild's sacrifice, Meliodas and Ban make it through the portal. However, as Ban is sent back to the real world, Meliodas is grabbed by the Demon King, who begins to drag him back to Purgatory, claiming that he can never be free unless Meliodas uses his true power but that Meliodas is too scared ever to do so. Meliodas simply smirks before destroying the Demon King's arm, allowing him to return to the real world.
Upon his return, Ban sets out to accomplish a singular goal before helping the rest of the Sins in their battles. Due to his body's adaptation to Purgatory, he's much stronger than ever before, now possessing the ability to grant his life energy to others. Though arduous, his time in the hellish realm has left a lasting, positive impression on him.