This seems rather strange.
If you set the draw out skills to any unit class other than samurai (with the requisite change to the action menu to katana inventory), you cannot use the draw outs. However, if your unit is controlled by the AI (either as a guest, or a setting like "save fading life"), your unit can use draw outs (even though you normally can't). For someone who knows more about this than me about the nature of the code, can someone check to see what portion of the spell's code checks to see whether a unit is controlled by the player? (I'm hoping this will be a lead to a way to circumvent the hard-coded blockade on the draw out skillset.)
that would probably help you repair elmdor's "sword spirit" which doesn't work unless the unit is AI as well...