User blog comment:TVthePunisher/409 - ...still on Decide I see.../@comment-117598-20100624004958

I for one am happy that Ichigo and Isshin don't share Zangetsu and that it's an entirely different spirit. I actually wrote somewhere else about my theory regarding their Zanpakutou's:

"i'm really hoping Isshin and Ichigo don't share Zangetsu. I would be much more happy if they were 2 entirely different spirits. Maybe spirits that are related in some way ( never seen an instance like that so its pure speculation ) but maybe Ichigo has Zangetsu, while Ishhin has a spirit that's close to Zangetsu, like Tengetsu or something like that. i don't know, just throwing that out there. Then if they had similar names and somewhat related spirits, it would explain why they both can produce a Getsuga... "

So i was off by one letter when it came to Isshin's spirit =)