The Eight members of the Sins were the strongest and most revered Holy Knights that others looked up to and the members this group were originally an independent order of knights serving the kingdom of Liones. They were declared as traitors and villains after being framed for assassinating Zaratras, the Great Holy Knight, after heeding an order to meet up with him at the castle.
But most didn't know about the eighth sin, Eris the Coyote's sin of strife.
She was named after Eris the Goddess of strife and discord.
Eris was commended as an elusive immortal assassin that struck chaos and strife into the hearts of many for her love of mischief and battle, making her good friends with Ban whom she's known for since the 8DS formed and Meliodas who she's known for a few thousand years.
***I DONT OWN NANATSU NO TAIZAI / THE SEVEN DEADLY SINS OR BLAKE FROM RWBY WHO POTRAYS MY OC***