User blog comment:Flamesword300/Overlooked? Ichigos true strength/zanpakuto discussion/@comment-5681812-20130621063411/@comment-5681812-20130621143505

@ sternritter. When Ichigo was almost giving up after soul society had been defeated, he told his dad that Aizen's reiatsu was way too much. His dad responded by telling him that he (Ichigo) was the only one who could tell the magnitude of Aizen's reiatsu, which indicates that Aizen has monstrous level of reiatsu. This is the level I think Ichigo's reiatsu will have reached after attaining bankai.