I can't exactly tell what her current story is outside of Iron's universe because it keeps changing every now and then, but as for what I made: Suwy is Weldey's little sister, and unlike her brother who goes around challenging people she would rather stay away from trouble as much as possible. However, that's not saying she's not a capable fighter in her own right and at most times shown that she may very well be a much better fighter than her older brother - though she herself claims that both she and Weldey just have different ways of approaching a fight, but Weldey would always be the better fighter.
She is also quite the beauty and capable of almost anything given to her, but the only reason she isn't exploiting her skills or even getting a boyfriend is simply because her life is busy on keeping her older brother from his recklessness. She dearly cares for him though and would do anything for his sake despite.
Suwy belongs to