well demons don't exist and you cant destroy nothing unless you put something real in it place so...
[IMPROVED ANSWER]
Sorry, whoever answered before obviously is rude and doesn't care about their answers. I care.
I have been researching it for a book I am writing right now, and demons (whether you think they are real, or need them for a story or any other reason) cannot deal with love. They are the opposite of angels, and angels sort of stand for love. Demons can't deal with love and therefore any act of love could kill one. Also, holy things. Holy water, holy blades, etc etc.
Demons, being angels cast out of heaven (therefore unworthy of heaven and the opposite of angels) can't deal with holy items either.
That is all I know of so far that would kill angels, I hope I helped :)
Humans can't kill a demon
When someone calls you a demon it means that you are evil.
erm your supposed to kill Elvarg which is lvl 80+, close to a lesser demon which is also about the same level In melzars maze you have to kill a lesser demon to open a door for a map piece.
The Sword you used to kill the demon with, the sword is good against demons.
by magic
Serena i have herd is a dream demon and tries to kill in your sleep. Contact with this demon is very rare and should try and contact a priest or wiccan to help banish this demon .
he is fictional doll with red hair, but not a demon. charles,l, ray, do some voodo before he dies, and turns into a doll, and he contine to kill, and kill, and kill.
you need at least a mithril armour to prevent dark wizards to attack you. With silverlight , you can kill it by 1 shot. (silverlight is weakness to any demon , including the demon you have to kill in mezler maze when you do dragon slayer.)
I think Inuyasha should stay a half demon because if he's a full demon he might lose control of himself and kill his friends.
meleethem
if the kyuubi was a card
3, there are safe spots there...