[DesuX2]

As of the latest chapter,

Spoiler for Possible Spoilers:

Kurosaki Ichigo is the son of Aizen. Aizen, Urahara, Isshin and all related to them are plotting to overthrow Soul Society.

Edit:

Spoiler for Spoiler 2:

Isshin is Aizen's teacher. Aizen can use Getsuga Tenshou. It was taught to him by Isshin.