who is isshin

[Munsu]

The one doing the inventions was Urahara, not Isshin...

[elmojo]

yea thats true, thats not what i meant

isshin left with him and urahara propably led the research division, so the only link to urahara's info was isshin himself and vice captains tend to snoop around on what their captains are doing, and as far as aizen is concerned, he's quite the intellectual villian so its very possible that he would snoop around

[SOLDIER [X]]

He had to have left before Urahara.

Important points to note:

-Rukia knows urahara
-If Ishin was there at the same time as Urahara's banishment he would look familiar to Rukia while she was living there.
-Urahara was banished within Rukia's time as a seated member of the Gotei 13
-Yourichi left before Rukia which explains why she does not really know her

Not sure if these are all true I read the manga last year and have been doing the weekly thing for awhile now.