Who is the Demon Lord? Place your bets now.
- The king is a bit too obvious, though 'avoiding obvious tropes' isn't something too many manga ever get accused of.
- It could be Clive. The 'invincibility' anti-magic power marking the Demon Lord either wasn't awakened during the fight with the MC, or was recently evoked with all of those cursed swords stuck into him. I could totally see Tristan doing something like that, in order to have the Demon Lord under his thrall.
- The best option would be for it to be Princess Sutra. Her abilities and thoughts are largely unknown to the reader. It would be a nice aversion to the expected 'harem get' route. Her never leaving the castle is kind of a Demon Lord thing to do. As the head of intelligence (pun unintended) her spies all over the place would make her pretty good at being the big baddie behind the scenes.
- The funniest would be if the Demon Lord were actually Tabla, the fat prince. Hear me out. He might not know that he's the Demon Lord, mostly because he's kind of stupid. The biggest evidence was way back when he first ran into the MC. Recall how all of his bodyguards were blown away, but Tabla was right there in the middle, unaffected but scared, creating a need for a 'wet floor' sign. It's like the MC's wind blast, though powerful, went right past him without even knocking him down.