Honestly, I think some folks get too tangled up in the dragon side of things. Acnologia's backstory hit me as a tragedy of human loss—the mage who watched everything burn. The 'Dragon Slayer' title came after. The lore implies he was a normal man, maybe a soldier or a scholar, living during the peak of dragon-human wars. The turning point was that cataclysmic event, whatever it truly was, that wiped out his entire world. He didn't just want power; he wanted to erase the source of his pain. That's why he consumed all that dragon flesh and magic, until he became the very monster he hated. The power corrupted him, but the grief started it. Makes him a more terrifying villain than a pure beast.
His status as the 'Dragon of the Apocalypse' feels earned. It’ sekai'd logic: the ultimate Slayer becoming the ultimate Dragon. They never gave him a sappy redemption, which I appreciate. He's a force of nature born from a broken man.