User blog comment:Godisme/Everything But The Rain/@comment-5695542-20130227204335/@comment-5398287-20130227230939

I'm not sure where you're getting this idea that Isshin was defeated by a Hollow before Masaki found him. We have no idea who or what he was fighting beforehand, and we don't know if Masaki fought that same opponent and won. So, no plot hole.