The high priest lifts an old and battered sword that gleams nonetheless down from its place on the wall. Turning to the kneeling paladin before him, he hands it down reverently.
"This is the greatest weapon of our order, it will serve you well in battle and never fail you against your foes."
"But revered one, are we not a pacifist order?" the young paladin bound for battle asks.
"Indeed," responds the high priest. "As the texts say, 'Do not hurt where holding is enough; do not wound where hurting is enough; do not maim where wounding is enough; and kill not where maiming is enough'." The priest hands the sword to the now rapt paladin. "As you well know, every magical sword requires the sacrifice of a life. Within this sword rests the soul of a great general who won many battles, but by the time of his death, he'd found war to be horrendous and abominable. He became a member of our order, and when he was near death, chose to be the sacrifice for a new sword.
"In the hands of one who wishes to kill, to make others suffer," the high priest continued, "this sword will not obey, and will avoid hitting the foe in any way it can. It will strike their shield, it will fail to even dent their armor, it will cause its holder to fumble. Even if used for a coup de grace, it will strike the enemy such that they suffer hardly any damage. But in the hands of one who is devoted to causing the least harm necessary, it will strike true. It will assist you in strike with its flat or pommel. It will turn your misjudged lethal blows into smiting but ultimately harmless blows."
"It takes great skill to wield a sword nonlethally," said the young paladin. They remembered the injuries they had both caused and suffered in training with other novices who had not yet learned the skill. "Even now, I often do not make attacks when I'm not sure I can strike true and mercifully." The paladin turned the sword over in their hands, feeling its compassion-like warmth.
The high priest nodded, "And so, this is why we entrust this sword to newly anointed paladins, who hold true to their oath and our ideals, but lack faith in their ability to practice them in the red fog of battle. This sword is not servant, nor is it master, it is companion and guide, and will teach you how to end battles not with death, but with compassion, and dealing only as much harm as is necessary to end the physical conflict." He took the sword from the paladin's hands and belted it around their waist, reverently, in an act of service that marks those who are truly the highest members of a church.
The paladin bowed their head and voicelessly prayed for their gods' guidance and faith as they were armed. Looking up, they spoke to the priest with the faintest tears in their eyes, "Thank you, father."
The high priest blessed the paladin with a benediction, and as they turned, he offered up his own prayer to the gods that his child would return safe from their battle.
The Pacifist's Blade
Weapon (Greatsword), Legendary (Requires Attunement)
This battered sword, seemingly once finely wrought, is a curse to the vicious and a boon to the merciful. In the hands of a character who seeks to kill their opponents, any attack made while holding the sword (whether with the sword or another weapon) is denied the character's proficiency bonus, as the sword veers to avoid causing damage to the opponent. In the hands of one who seeks to subdue an enemy without killing, the sword strikes true and provides a +3 bonus to attacks and will not kill an enemy. If the wielder then chooses to kill their opponent when they reach 0 hp, the sword rebels, and refuses to land that killing blow (they target is still reduced to 0 hp), and thereafter the character takes the penalties of one who seeks to kill above until they have properly atoned (generally through roleplayed counsel with the spirit of the blade and a period of receiving no bonus from the sword while engaged in non-lethal combat).
The Pacifist's Blade is also sentient, holding within it a soul. It does not speak (though it might shout in the old general's voice in fitting or dire moments) and instead only converses with it's wielder telepathically. It has normal hearing and vision out to 60 ft, is Neutral Good, and has 14 Int, 16 Wis and 14 Cha. It seeks to prevent the horrors and atrocities of war through ending conflicts before such things happen.
Because the sword is intelligent, its wielder can appeal to it when they feel that one act of killing is necessary to prevent the deaths of others. Treat this as you would normally handle the wielder convincing an NPC of something (if the sword is convinced, it will provide its normal benefits even when the death of the specifically discussed target is sought). However, if it seems that its wielder is always killing with the excuse of preventing more deaths, the sword is smart and wise enough to recognize this as a trick and may rebel.
The Pacifist's Blade has Deathwatch constantly active, can cast cure wounds (2d8+3) 3/day, and can bless its wielder and their allies 3/day, as well as cast globe of invulnerability once 1/day. As an item with a special purpose, the sword can also cast true resurrection on its wielder 1/month.
Note--Deathwatch is a spell from 3.X, where it is, weirdly, an Evil spell. It should not be evil, as all it does is act like a magical EKG monitor. The relevant information is:
Deathwatch: You instantly know whether each creature within the area is dead, fragile (alive and wounded, with 3 or fewer hit points left), fighting off death (alive with 4 or more hit points), undead, or neither alive nor dead (such as a construct).
3.X rules
In 3.X, the Pacifist's Blade is a nonlethal weapon. When used to inflict lethal damage, the wielder suffers both the normal -4 penalty to using a non-lethal weapon to inflict lethal damage and a -4 penalty from the magic of the sword (it is effectively cursed). When used to inflict non-lethal damage, the sword provides a +5 enhancement bonus.
The Pacifist's Blade is an intelligent item with Int 14, Wis 16, Cha 14, which can communicate telepathically and is able to speak, but seldom chooses to. It can see and hear normally, and seeks to prevent unnecessary suffering. The Pacifist's Blade has Deathwatch constantly active, can cast cure moderate wounds (2d8+3) 3/day, and can bless its wielder and their allies 3/day, as well as cast globe of invulnerability once 1/day. As an item with a special purpose, the sword can also cast true resurrection on its wielder 1/month.
The Pacifist's Blade has an Ego of 24.