this story is a wasted opportunity(common amoungst manhwa) if upon possessing the son the sword then spoke to the father in a one-on-one situation and made clear:
1: his son is dead
2: if he isnt restored to the inside of his sword it will remain as nothing more then a nice sword
3: pursuing 2 requests that he is executed by said sword
then the story would have gone in a far more interesting direction. the father would likly come to the conclusion the execution to be too rash a decision and negotiated a different plan perhaps even annocing that his son is dead and his new heir is the spirit of their ancestral sword
not only does this make a more interesting and fresh relationship between MC and his 'father' but also sets up his personality to be rather alien to what one would normally expect of a MC which would also be its own kind of interesting