X3 I'm not sure how Hojo got Sesshoumaru. Maybe he trawled him out of the Lifestream or there was some kind of weird trans-dimensional experiment. Or maybe it was something on the IY side - something Naraku did or a botched(or successful!) exorcism.
(And quite possibly! X3 And there would be much sword-envy on Sesshoumaru's part over Seph's Masamune)