"Omae Gotoki ga Maou ni Kateru to Omou na" to Yuusha Party wo Tsuihou Sareta node, Outo de Kimama ni Kurashitai

Flum has been chosen by God to be in the hero's party despite having stats of zero across the board. All she has is the "Reversal" ability that she still doesn't fully understand. Predictably, she proves useless in battle, but she refuses to give up and continues to do all she can for the party. Her partymate Jean, a genius and renowned sage, picks on her at every opportunity and eventually sells her off into slavery. Even as a slave, she's treated as incompetent and persecuted, and ultimately thrown to monsters as bait for her master's entertainment. Flum is left with two options: take up the cursed sword that inevitably brings death to its wielder, or be eaten by monsters. The moment she chooses to fight back is when the "Reversal" of her life begins...

(Source: Crunchyroll)