Twins, But Not Really (Edward Elric X Reader...
(y/n) and her sister tried to bring back their mother with human transmutation, causing (y/n) to lose her leg, and her sister to lose her entire body. (y/n) then lost her arm binding her sister's soul to a suit of armor. They later went to Rush Valley for automail, and years later, met the Elrics.
(Ahahaha, this is so cleche XP For those of you out there that have already read/seen this, I changed the title because I've noticed several other's with the same title.)