I don't if this speculation has been tossed around at all, but I have a hunch Kyros has turned into a toy, our beloved Thunder Soldier of Rage. Now you might think this could be any toy by now.
Kyros' page says the following:
Kyros was a legendary gladiator.
No one knows if he actually existed -> everyone has forgotten him. This would mean he definitely turned into a toy. That part is clear as day.
Now for my reasoning as of him being TSOR:
20 years ago TSOR must have been a young adult (old enough to have Rebecca, young enough to be Riku's son(-in-law), so he must've been 20/30-ish of age. If Kyros vanished 20 years ago and TSOR found/saved/protected Rebecca 10 years ago, it would add up. The 10 years of raising would fit in the 20 years of being a toy.
What do you guys think?