The Demon King Who Lost His Job - Ch. 340

[MangaDex]

 

[Kjack49044]

I'll make a wild guess, through some time travel shenanigans Merlin will end up going back in time and becoming the prophet of demons guy. That way he's actually the only guy in history to draw aeternium, and it was always made for him. Bonus points if he meets his mom while she was younger and convinces her/tells her how to have him later in life