Etwahl is a cursed vessel harboring the spirit of Mordekaiser's wife.
Etwahl was part of Thresh's collection prior to the Ruination.
Evelynn was allowed to leave the Shadow Isles in exchange for finding a new owner for Etwahl. (I could explain more about why Evelynn was here, but I won't.)
Evelynn sold Etwahl to a merchant in Ionia. He in turn sold it to another man that gave it to his brother as a belated wedding gift.
The merchant died in a mugging only days before the wife passed away during childbirth.
The father finds it odd that his daughter does not weep or cry. Doctors confirm the child is mute.
Over the course of the next couple years, the father struggles to provide and care for his child. He has help from his relatives, though he does end up selling many possessions. It never crosses his mind to part ways with the Etwahl at first. When it is suggested, he admits he cannot part ways with the gift for sentimental reasons.
Strangely the relative that suggested this course of action falls ill and passes away.
Upon her second birthday, Sona takes an unusual interest in Etwahl. Her grandmother, whom watches over her in father's absence, gradually becomes fearful of this. It culminates into hysteria after learning her older son, whom purchased Etwahl, died in an unusual accident at work. She is summarily disposed of without a trace.
With the family refusing to help, the father does all he can on his own. He quickly falls into debt due to his inability to work and watch over his child. With threats upon his life, he abandons his daughter shortly after her third birthday and is never seen again.
Much of the old lore is preserved from this point, though Etwahl isn't nearly as "forgiving" about being parted with its host. Usually the primary caretaker is subdued and won't consider selling Etwahl, though subordinates might be less considerate at their own peril.
*** Quick Edit
Also want to point out that Evelynn actually held onto Etwahl for a long time. She had no real incentive to sell the thing and she was immune to Etwahl's influence.