It's probably improper to call the demon race "demons", and for the demon race to call itself the demon race, while also insisting that everyone gets along.
I'm 99% sure they're using a term like
魔族, which means everyone and themselves are calling them evil. I'm not suggesting that there's going to be a twist or that this is a dangerous insistence of the protagonist's-- I'm criticizing the writing for not addressing that peculiarity.
And I probably wouldn't have even minded if the story was more than "barely interesting" (a shame for a yandere story).