Another Felix

Another question: is there a way to repair weapons? I don't want Lon'Qu losing Killing Edge.

nope - only a super rare Hammerne - Staff (or however it is spelled), and it only has or two uses

I think you get one pretty late somewhere in a chest during a story mission... or randomly (but also super rare) through Weapon-grind DLC

just give him an Iron or steel sword and use the killing edge only for super annyoing things that absoluteley have to die

you can use the wireless feuture to give yourself Lief's blade, which is a weaker killing edge. later you reach a place where you can just buy the weapon