Prior to the start of the final duel between Anos and Ray, the owl MC fitted Anos with a Spirit Drain Ring that saps his Magic Power. If that power is depleted, Ray’s mother will die. If he defeats Ray, the contractual Magic Sword will destroy his source.
Ray decides to damage the contractual sword himself anyway, breaking his contract and leaving him with nothing but his fight with Anos. It’s a duel they both wish to fight for its own sake, not for any outside stakes.
When Anos stabs Ray through the chest (at the cost of his own arm), he learns that both the contractual sword and his participation in the tournament was arranged as part of a plot to eliminate him for good.
The author of this plot? Melheis, who promptly locks Anos in a dimensional prison with more than half of his Magic Power drained.
Melheis seems to have thought this plan out very thoroughly, as it employs multiple contingencies, from the use of Ray’s mom as a hostage to creating an “Absolute Space” where he and only he can reside, thus preventing him from ever being defeated.
He even saved a part of the wall Anos himself used to divide the world into four. What Melheis overlooks is the fact Ray had already made peace with the fact he wasn’t going to be able to save his mother no matter what.
That, and that by bringing his mother into the dimensional prison, he brought the one person who could destroy Ray’s pessimistic resolve with hope and love. She remembers when he slashed a pot with a kitchen knife. Now she becomes a sword (her true spirit form) with which he’s able to slash the un-slashable Absolute Space.
Melheis’ third and final mistake is attempting to eliminate Anos with Beno Ievun (the wall spell) after sapping so much of his Magic Power. Rather than the intended effect of killing Anos, it instead releases a limiter of sorts that had resided in Anos’ Destruction Source. Anos had never faced quite this much peril, so the true depths of his power had been limited…until now.
With that power he summons Venuzdnor, chops Melheis’ legs off, and destroys the prison. He then destroys a tiny Sword of Subordination that was attached to Melheis’ brain, thus explaining his sudden heel turn. With that brain bug destroyed, Melheis is again loyal to Anos.
The duel ends with Anos as the winner, and he makes a very loud and precise speech to all the assembled spectators in the arena and throughout the land crediting his victory to his sword, which contained his father’s very soul.
By doing so, he’s able to create the “tradition” of souls within swords that enables him to heal Ray’s mother’s source and revive her safe and sound (again, her true form being a sword). Ray never had to choose between his life, his mom’s, or Anos. Go fam!
All that’s left is the presentation of Anos’ trophy sword, which has always traditionally been performed by a Necron, hence Sasha making a last-minute appearance in an exquisite dress and a very cute alternate hairstyle. While she initially coldly holds the sword out to him, when he asks her to stick to the script she draw close and kisses his cheek.
Sasha took the job because she knew Anos would win, and she’d never accept any Demon King but him (though we may have gotten our first glimpse of the usurper Avos Dilhevia). Misha, meanwhile, never one for jealousy, simply asks if Anos had fun. He did!
Demon King Academy turned out another baroque magical skirmish that threatened to collapse under the weight of its arcane magical jargon. But just like the battle that saved Misha and Sasha, everything was held together with a solid emotional core, carefully prepared and supported by previous episodes.
Anos isn’t just an all-powerful Demon King. He’s a son who loves his mom and dad, and can and will do anything and everything for his friends. His enemies, while crafty, lack that sense of family unity and are instead held together by a patchwork of defeatable spells, trinkets, and fear; all easily defeatable. That’s why Anos always wins.