There’s a spell in GURPS Magic called Weapon Spirit on page 64. In short, it gives a weapon an IQ score, and can communicate with empathy or, with the right spells, speech. That’s pretty much it. There can be other spells on the weapon, but you can always do that. The weapon could have some disadvantages, which would truly piss off a player.
Forgive me, but what a goddamn bother. Brains in a sword should give you a boon for wielding it, not just giving you a talking metal buddy that might not like you anyways.
So, these are two simple things any intelligent weapon can do that shows that it has a brain:
- Anyone who has an intelligent weapon Ready can Dodge attacks from behind him (p. B391), at -2. For those attacks from the side hexes which he normally must defend at -2 (p. B390), he defends at -1.
- If you hit when targeting chinks in armor (p. B400) with an intelligent weapon, you get through all DR, not just half DR.
The wielder must get a reaction of at least Neutral the first time he picks up the weapon to get these boons (or any others tied to the sword’s intellect). These boons show things the sword sees and understands and lets its wielder know.
Smart weapons are fickle. Remember, they need a reaction roll to use. Charisma and Born War Leader will always impress a weapon; Appearance and Voice do not. Status might; your call.
Let its Will be its IQ plus its highest level of Puissance or Accuracy. The wielder is -1 to Will checks against the weapon for every 1/4 HP or FP he is down. Control checks are a Quick Contest of Will. Check when:
- The wielder has a chance for another magic weapon
- One of its disadvantages comes up (see below)
- The wielder drops below 1/3 HP or FP
- Someone with a higher weapon skill is available to own the sword. Use skill plus maximum basic thrust or swing damage, as applicable.
If the sword wins the Quick Contest, it will make the wielder bypass the other weapon, abide by its disadvantage, keep fighting even if the wielder has lost most of his HP or FP, or drop his weapon to let the higher skilled fighter pick it up.
If a sword has a disadvantage, it expects its wielder to abide by it, and will try to control its wielder in case of any conflicts. The sword gets a bonus to its Will rolls to control its wielder regarding its disadvantage, and this bonus is equal to the penalty to Fright Checks for Phobias at each Self-Control Number, read as a positive. Thus, a sword with Honesty (15) gets a +1 to Will rolls to make sure its wielder behaves honestly, while a sword with Honesty (6) gets a +4 to the same rolls.