Hypno-girl said:
There is only 3 choice at this point:
-It is Zangetsu
-It is another zanpakuto
-It is not a zanpakuto
The way it ressemble Zangetsu suggest that it is either Zangetsu or a similar Zanpakuto hence why I tough that it could be Engetsu or an heirloom from the Kurosaki family.
( By the way was it said that Kurosaki is really Isshin's name? It could be an alias that he took once he decided to mary a human or perhaps he took his wife's name when he maried. )
Anyway we do not know what Urahara inserted inside Ichigo because it looked like everything but a zan. It could be the materialisation of Zangetsu itself or another zanpakuto's soul, it could be a kido or simply something else.
Do you think that Isshin is actually part of those Noble Family from Gotei 13??
That's pretty interesting,, and quite reasonable since, as i remember, we haven't know all of those Noble Family names.