I'm sure this was brought up before but.....
They mention that there are 4(?) families of SS we know one is that little princess, another is the family that adopted Rukia and there is a 3rd and 4th...dont they mention that 1 of the families has disapeared or not been heared from? Is it possible that is Ichigo's father?
It seems teh popular theories are:
1. His father was kicked out with the other 2
2. His father faked his death