Board Thread:General Discussion/@comment-7779702-20130404000656/@comment-5551986-20130424095646

Zabimaru's release command is Howl [Roar]. I highly doubt Renji's "Ace in the Hole" is a gigantic sword roar, I think the release command defines a Zanpakuto's personality slightly, not necessarily the ability. Although that is just a swing in the dark really.

I just think Isshin's Zanpakuto (If you defined it as a straight up ability like Fire, Ice, Earth, Illusions etc.) I would assume its a type of Reishi manipulation to augment attacks, In a similar way to Getsuga Tensho, but it has different levels, and attack variants. That or its just a straight up melee type, and he can channel attacks in different ways like Ichigo can (Holding Getsuga in his sword to improve its melee)