User blog comment:Apocaylpse06/Ichigo Kurosaki's (New) Zanpakuto/@comment-3010659-20110817104256/@comment-3010659-20110817185858

I was thinking what Salubri said.One can't use his Zanpakuto's powers in its sealed form so we have to agree that Isshin used his shikai to cast Getsuga Tenshou at Aizen.