The spirit following him is wrong, the maid is not an assassin but a subordinate of the demon lord. And it just so happens that the MC is the grandson of the demon lord who is about to die, and needs the MC alive to be his successor.
The son of the demon lord (MC’s father) is already dead and the dad living in his house has been replaced by a homunculus that works for the king of the country who is secretly evil and is being controlled by a demon that knows mind control magic that will be more important later in the story.
What the spirit meant by making the MC disappear is that the maid will kidnap the MC and go through that armory door, the thing is, it’s not an armory door it’s a flight of stairs that goes straight to the demon lord’s castle. At the same time the maid will secretly brainwash the mom and the homunculus dad into thinking they never had another son, wrapping up all the loose ends.
The author has an unlisted youtube video that covers that this is all of his plans for this manga that’s only for his pixiv fanbox subscribers which is here: https://youtu.be/-51AfyMqnpI Please LMK if this is the correct link, I’m still new to mangadex.
And then manga is axed because this is a terrible storyline that was completely made up by me in the last 5 minutes.