That's no moon!
I get the feeling that the Shota ancient demon king is going to stick around for a long while as the main super villian and umm, that kinda bores me. He's not that interesting or charismatic or even that threatening (despite him being stupid powerful; he kinda just falls into the trap of being one of those really strong characters that are just a brick wall to overcome). I mean maybe I'd care about how he killed the other isekai high schoolers... but no. Not really. None of them were that well developed either. So it's just like cool, whatever. I mean hopefully we can at least get some character motivation because right now he's just Disney villian evil. But like not doing fun musical numbers.