The Misenchanted Sword

Valder is just a simple soldier in the army of Ethshar, on a simple scouting mission. When the enemy attacks in force, Valder is trapped behind enemy lines with a patrol chasing him. He then inadvertently stumbles upon an elderly hermit wizard, and the result is that the wizard's hut is destroyed by the enemy patrol.

The wizard, wanting nothing more to do with Valder, makes him a deal: he'll enchant Valder's sword, enabling Valder to return to his unit, and Valder promises to leave the wizard alone. The sword is enchanted...and what an enchantment it is. The sword is capable of killing anyone it's used against, and in fact Valder cannot be killed while he uses it.

Too bad there's a drawback...

The Misenchanted Sword, first of the Ethshar fantasy novels by Lawrence Watt-Evans, details Valder's misadventures as he struggles to adapt his life around the power of his sword Wirikidor's enchantment...and the desires of those who want to take advantage of those powers.

Tropes used in The Misenchanted Sword include:

• Action Survivor: Valder, not being particularly skilled as a soldier.
• Age Without Youth: Part of Wirikidor's enchantment.
• Awful Truth: It turns out that Ethshar disintegrated into tiny squabbling feudal kingdoms long ago. The army had been carrying on the fight against the northerners for generations, with only the generals aware of what had happened.
• Brick Joke: The entire novel could be seen as the setup for one.
• Career Killer: Valder ends up being forced into this.
• Clingy MacGuffin: The sword.
• Deal with the Devil: The northerners made several. Then the gods took notice.
• Distant Finale: Takes place 160 years after rest of the novel. Valder is still running his inn.
• The Empire: The northerners, complete with The Emperor.
• Fish Out of Water: Valder at first, adapting to peacetime life.
• Give Chase With Angry Natives: The protagonist -- a soldier behind enemy lines -- takes a nap in a tree, and when he wakes up, there's a young dragon on the ground beneath him. He jumps on the dragon but is unable to kill him, so he runs away through the forest, the dragon chasing him, until he finds himself unwittingly on the edge of a large enemy encampment. He screams and runs through the camp -- and the sentries, soldiers, etc. who start chasing him have to turn around to deal with the dragon.
• I Just Want to Be Normal: Valder eventually becomes this, as his work as the army assassin eventually gets to him.
• Immortality Inducer: The protagonist is a cowardly scout granted this by a magic sword. He believes he "cannot be defeated until he has killed 100 men", and puts his sword down and retires long before reaching that number. He doesn't find out the truth for... quite a long time. He cannot die until he has killed a hundred men.
• Immortality Hurts: The sword grants its owner eternal life so long as they retain their ownership. However, this portion of the magic has two staggering flaws: First, it doesn't prevent the wielder from aging, and will in fact prevent a natural death. Second, it will only prevent the wielder from dying; it is perfectly alright with letting them be maimed, blinded, or any number of other horrible things that happen when one wields a bloodthirsty sword.
• Loyal Phlebotinum: Wirikidor to Valder, although said loyalty has its limits. Most of the plot is centered around getting around these limits.
• The Magic Goes Away: According to General Gor, the gods shut themselves away after sealing away the demons and ending the Great War. While Gor makes it clear this doesn't mean all magic vanishes, he does say magic might not work the same - at least, the theurgy and demonology branches of magic, which deal with gods and demons, respectively.
• My Grandson, Myself: Valder, after gaining eternal youth, poses as his own nephew to ensure that the inn remains his. After that he continues to use this ploy: he owns two inns and every so often switches which one he runs himself, then later returns to the other claiming to be his own son.
• Our Demons Are Different: The shatra, who are technically half-demons, are considered nigh-unkillable by almost everyone. Of course, almost everyone does not have Wirikidor. There are also full demons, but they never show up directly in this novel (some of them do turn up in other Ethshar stories, though).
• Our Gods Are Greater: Apparently they are all Actual Pacifists. They break their oath once, to seal the demons and kill those who summoned them.
• Really Seven Hundred Years Old: The 288 year-old Iridith, who looks to Valder to be about 25.
• Situational Sword: The sword will do your fighting for you, but only against adult male humans, and once it kills, you have to sheath it and draw it again to re-activate its power. Also, you can't resheath it, or even let go of it, until it's killed someone.
• Who Wants to Live Forever?: Subverted. Certainly not Valder, but the alternative is worse.