[Zu Ra]

Originally Posted by alsy333

In the first manga chapter Ichigo asks his father why the samurai dressed person (refering to Rukia) got in the house so easily. Isshin said he didn't see anyone and didn't know what Ichigo was talking about. But later in the series we find out Isshin was actually a Shinigami. So was he just pretending when he said he couldn't see her or what?

The manga expalanation of this is

Spoiler for manga:

Isshin's powers were sealed away and they returned completly in the second season . Due to this he sesnses that Kon is in Ichi's body . Sealed was the explanation that is revealed during Isshin's convo with Ryuuken

Coming to your question Isshin cant sense/see Rukia as his powers were sealed away . At what point of time his powers began to return is unkown but definately not the first ep