I'm finally caught up!! This manga has been a completely pleasant surprise for me and I've enjoyed a lot of it thus far. I don't have much to add in regards to theories that others have not put out before but I think we're probably going to see that finishing the medicine isn't enough and the last push has to come from Albus.
The story thus far has had a lot of focus on relationships and how the Hero vs Demon King conflict was experienced by many people before Albus. Relationships drive the Hero to end the Demon King. Even the First Hero has had (fond?) things to say about his friendship with the sorcerer before he became the Demon King, comparing him to Albus and Rayman, maybe that's why he's so dead set on putting the Demon King to rest.
It makes me think in a 'perfect future', perhaps the Demon King, and therefore the First Hero, are also saved. The First Hero cannot move on if the Demon King exists as it does, and if Albus finds out God's Messenger was actually a human all along, I'm sure he'd want to save them, too.
Simple parallels like this give our protagonist so much potential to grow while adding depth and intrigue to the Demon King's past. There's also Zealark (my fave), who makes the story interesting (hehe, see what I did there) just by being around. Anyway, I can't wait for the next chapters. Thanks for the awesome translations so far!