Okay, so yes, Raiko is for sure aware that he is a half demon but he isn't aware of what kind of who his parents are or what type of demon he is. This, I think, will provide for some nice reveals later down the road. But, I do think on some level he be aware of it. All I know is that, for his demonic abilities, he will kind of just know it. Like, he won't be able to tell you who his father is or if he is a dragon demon or whatever, but there'll be this part of him that will just know.

As for Ren being aware, I'll leave that up to you. If you wish to have her aware or not, that's entirely up to you. 

For the villagers, I actually want them to know and to accept him because the meaning of "seiki" is sanctuary. I think this would be one of those villages where they take care of their own. In that, it would mean they don't care if Raiko is a demon or not. He grew up as one of them and despite his demonic nature, he is one of them. For better or worse, he has sanctuary within Seiki.

And yeah, at his current age, Rai is still very early in his power development. So if something were to happen where he would use them, it could potentially result in something bad for those on the opposite end. >:]