Given your studies of the King's work, you can glean the understanding that the magic and the weapon are so closely intertwined that you need to break the trident itself in order to get rid of the magic. The rune you can shatter by breaking the actual symbols! However, it'll take a lot of firepower to do so, and there are a ton of shadow creatures around it.

It looks like the majority of them are coming from the King, but it's hard to tell with all the chaos.