Can you select a given creature as your Familiar? If so...
Polymorph Sword into a Toad->Declare the Toad as your familiar->allow Polymorph to wear off.
Also, what kind of arguments would you be able to make that the sword itself could be gestalt? If you can get it approved, gestalt Spellthief and Rogue.
Get polymorphed into a cat or something->Have the Katana declare you as a familiar->let Polymorph wear off.
Voila, you can steal random spells and/or buffs from enemies every time you attack.
If your Sword steals a spell effect, it transfers it to you, and then ends the effect on itself. You share it back, so that the buff doesn't count against spells steal-able.
Also, you get 10d6 SA damage thrown on.
Of course, this is all cheap, so you could get one katana that's a cleric, and another that is the above spell-sharing spellthief abuse. (I like the second one. It is sexy from a "this is a DEADLY sword perspective.")