Either way a demon can die

Key things

• Exposure to sunlight or sunrays infused weapons (Nichirin) is critical to killing demons in Demon Slayer.
• Wisteria poison can paralyze demons and in stronger doses kill them.
• Starvation can work as a last resort, other weaknesses like Marechi blood or Blood Demon Arts can also hurt demons.

Warning: The following contains minor spoilers for Demon Slayer: Hashira Training Arc, now streaming on Crunchyroll.

IN Demon SlayerMuzan's army of nearly indestructible demons is the greatest threat to humanity, but “almost” indestructible means there is still hope. While conventional weapons cannot kill demons, it is well known throughout the series that they disintegrate almost instantly upon contact with sunlight. However, there are other ways to kill demons; and while they may not be as reliable as sunlight, the demon slayer needs every advantage he can get if he wants to stand a chance against Muzan and his maneaters.

Cut their heads off with normal weapons, blow them up or burn them; all these things that are deadly to normal humans are mere nuisances to even the weakest of demons. If you want a one-off finish permanently, you'll need to rely on one of these methods.

How to kill a demon

Sunlight and Sunlight Infused Metals (Nichirin Weapons)

That being said, the most effective way to kill demons Demon Slayer is to expose them to sunlight. Sunlight makes people completely safe from demons during the day, but it does no one any good at night unless you are a naturally gifted fighter who can hold off a demon until sunrise.

But if you they are gifted fighter, there is a better way to use sunlight. An indirect way to expose demons to solar power is through Nichirin's weapons of the Demon Slayer Corps. What makes these weapons special is the materials they are forged from, known as Scarlet Ore and Scarlet Crimson Iron Sand, which are mined in the high mountains where they can absorb the most sunlight. Due to the natural sunlight within them, Nichirin weapons can be used to slay demons, which can range from swords to maces to sawed-off double-barreled shotguns. However, since it is only indirect contact with sunlight, the Nichirin weapon must decapitate or destroy the demon's head to kill them. The demon can still heal any other body part damaged by the nichirin weapon.

Fun Fact: Iron sand is an actual type of sand that heats up when exposed to sunlight and can get hot enough to cause minor burns when touched.

Wisteria poisoning

Beautiful wisteria plants often decorate the bases of the Demon Slayer Corps and sometimes the homes of its members. But these purple flowers aren't just for show; they are the main ingredient in a special poison that the Corps uses against demons. A normal dose of wisteria poison can paralyze demons, limiting their abilities, movement, and even their regeneration. High enough doses will kill demons outright, although larger doses are required the stronger the demon.

Have you ever noticed how strange Hashira's insect, Shinobu Kocho's blade looks? The shaft of her sword is incredibly thin except for the base and tip. You'd think she'd have trouble slashing with it, and you'd be right, since Shinobu uses the blade to stab demons rather than slash. The scabbard of the blade houses a powerful wisteria poison that coats the sword he uses to slay demons in gruesome and painful deaths.

Interesting fact: Wisteria flowers are real, but they are also poisonous to humans.

Curse of the Kibutsuji

To protect his identity, Muzan Kibutsuji placed a curse on each individual demon that would be triggered when they revealed any information about him. Even just saying his last name can cause the curse to take effect and kill the demon that said it. IN Demon Slayerseason 1, episode 10, “Together Forever”, a demon named Susamaru accidentally spoke Muzan's last name while under the influence of Tamayo's Blood Demon Art and in a fit of rage. Shortly after, arms burst out of her mouth and torso, crushing her to death. However, revealing information about Muzan is not the only way to trigger it, as Muzan himself can activate the curse in any demon whenever he wants. It seems that even a curse can manifest itself in different ways. Muzan can just explode the demon and be done with it.

“You said his name out loud, didn't you? You just activated his curse” – Tamayo Susamaru

While this is technically a way to kill demons, it's not easy for a demon slayer to take advantage of because it relies on the demon making a mistake or being under the influence of something like Tamayo's Blood Demon Art.

Starvation

Starvation is the ugliest way to kill a demon Demon Slayer as it is the only method not seen in action in both the manga and anime. In fact, the only source that suggests demons can even starve to death is a quote from Tamaya. She states that since she changed her body, she no longer needs to feed on humans to survive, implying that the other demons will eventually starve to death if they stop feeding on human flesh.

Starvation is also not a very effective way to deal with a demon, because if one has the ability to subdue a demon, it is better to wait until sunrise and kill it with sunlight. If a demon's metabolism is similar to that of a human, it can take weeks for them to succumb to starvation. That's probably why no one has ever seen it before.

Other demon weaknesses that damage them but don't kill them

Marechi blood

Marechi blood is a rare blood type in humans that contains about 100 times more nutritional value than normal human blood. Its power causes demons to go berserk when they get a whiff of it, attacking recklessly and making their actions more predictable for a skilled slayer. Sanemi Shinazugawa, the Wind Hashira, has Marechi blood running through his veins and will make full use of it in the upcoming Infinity Castle Arc.

Blood Demon Art

Higher level demons have abilities unique to them, known as blood demon art, and ironically, it is this power that can be used against their own kind. The best example of Blood Demon Arts being used to harm other demons is Nezuka's flaming blood, which produces bright pink flames harmful to demons but not to humans. Tamayo also armed another Blood Demon Art against Muzan himself at the end of the Hashira Training Arc. Of course, any demon harmed by the Blood Demon Art will eventually regenerate from it, as only Muzan is capable of killing his own kind.

Demon Slayer is now available to stream on Crunchyroll and Netflix. The release date for the next season of Demon Slayer, the Infinity Castle Arc, has not yet been announced.