[quote=WitchChild]
It was also going to be something to give my character a drive to do something other than just learning magic but means to get more godstone and ways to mend the sword. He doesn't want to have a broken prison as a weapon where the prisoner is trying to kill him at a daily basis. Not to mention tormenting him through nights via visions of a giant snake devouring the world. And then there is the weight that it's the character´s responsibility to carry the sword due to family sense of honor and what not.
[/quote]

Fine. Let it be a broken prison. Let it be tormenting nightmares. Let it be weight of responsibility and what not.

One condition. 

One: It's a normal sword. The part holding the demon will be a cracked Gem in the hilt that can't be repaired through any known way. It's not a magic slaying sword, it's not a godstone sword. It's simply a a sword with a demon in it that's really pissed at being trapped, and has now found a way to try and work his way free.