Each member of the Seven Deadly Sins had been judged and found guilty of committing a grievous crime by the Kingdom of Liones, with their title being given based on the root moral failing on their part which caused this crime. Though it sounds clear cut, for most of them it seems extenuating circumstances were at play.

Meliodas
Meliodas considers his sin to be his failure to protect Danafor, its citizens, and Liz from the kingdom's annihilation.[7] The official story is that Meliodas lost himself in his wrath and annihilated the Kingdom himself.

Diane
Diane and Matrona were hired by knights of Liones as mercenaries to assist them in a battle against foreign savages. The Holy Knight Gannon deceives them, revealing his ultimate intentions of taking down a giant for reputation and prestige. Although Matrona unfortunately "dies" from a venomous arrow, Gannon underestimates her strength and his plans are thwarted. The giantess "passes away" after killing the majority of the troops including Gannon, with remaining survivors falsifying the report of the incident to place blame on Diane. She is eventually labeled the Sin of Envy for her jealousy towards Matrona (who she supposedly murdered) along with 330 innocent knights of the kingdom. She is sentenced to death by beheading but Meliodas thwarted it under direct orders of the king of Liones.

Ban
As the only survivor of the Fairy King's Forest, he took the blame and was convicted for destroying the forest and killing its guardian saint, Elaine. As a result, he was sentenced to death, and became known as the Sin of Greed due to his apparent greed for immortality.[8]

King
After supposedly ending Helbram's life, King took on the sentence for ignoring Helbram's mass murdering of humans continuously over a period of five hundred years. This came close to sparking a war between humans and fairies. He was consequently sentenced to an imprisonment for a thousand years, and was recognized as the Sin of Sloth as he ignored the atrocities committed and turned a blind eye.