Watching the anime after reading the manga, the demon's connection to the prophecy felt like a slow, chilling reveal. It’ Soyriously emphasized in the Spade Kingdom arc, where the Dark Triad’s plans are explicitly about fulfilling it. The demon, Lucifero, isn't just some random big bad; his very existence is the core of that 'end of the world' forecast. The prophecy talks about a devil with the power to end all things, and that’s literally his schtick—gravity magic so overwhelming it could crush continents. The link is direct cause and effect.
What gets me is how it retroactively colors everything. Asta’s demon, Liebe, being a powerless anti-devil creates this beautiful paradox. The prophecy assumed a supreme devil would bring ruin, but the actual threat stems from the despair and ambition of humans trying to harness that power. So the demon is linked as both the literal subject of the prophecy and the symbolic embodiment of the fear that drives it. The story subverts the trope by making the 'fulfillment' hinge on choices, not destiny.