User blog comment:TheBody84/Ichigos father being the former Kenpachi/@comment-1403595-20091025111628

Well really, considering that some of the lieutenants didn't even know some other squads captains (as seen in the convo at the vice-captains meeting at the beginning of the Ryoka invasion, SS arc), Rukia not knowing Isshin makes perfect sense, a rookie would hardly be expected to know all the captains. Secondly we don't really know that Matsumoto has spent her entire career in squad 10, she might have followed Gin into squad 5 to begin with. So realy, recognition has little to do with it.

Having said that, I am beginning to doubt the Captain of 10th squad theory as I write, considering that Yamamoto, of all people will know every captain that has been in the past 2000 years, and Isshin is recently a captain, so he would be expected to react to the name Kurosaki, if it was Isshin's name. The other thing to think about is Ichigo's resemblance to Kaien Shiba, perhaps Isshin has some connection to the Shiba family by blood. This is getting far more speculative as it goes but Kubo has left all these tantalisingly annoying hints scattered throughout the manga.

My major doubt about the Royal Guard theory is that Isshin does wear a captains haori, why would the Royal Guard wear haori's? Surely their uniform would be different to distinguish themselves from their past jobs. As each haori has a squad number on the back this is, I think, minor evidence towards him being an ex-captain not ex-guard. It also wouldn't surprise me if Aizen was involved in his exile, although it would be a bit boringly predictable.

@Bk1217: It's a filler. We can't "know" that it really is electricity type until the manga shows it. In the games for a long time, Kyoraku was depicted as having a wind type zanpakuto but we were proved wrong. Until it's manga, we can't be certain that it's just something to fill in the gaps. Also, note that Tenken, Komamura's sword, breathes fire yet his zanpakuto has no such ability when he wields it.

Hisagi's is as dual bladed as Ukitake's is, as Ukitakes are also joined at the hilt. Hisagi does also wield both blades simultaneously, so it isn't like he uses them alternately and could be classed as a one blade zanpakuto. The reason is probably that 1) Kubo hadn't thought of Kazenshini at the time he drew Yamamoto and Kyoraku/Ukitake's fight and 2) That Hisagi very rarely releases his zanpakuto and Yama might have been unaware of it's form, he can hardly be expected to keep tabs on the power of all his underlings.