Nice story but its plot slightly seems like harry potter, i don't mean to hurt you or anything. I like your story, but lately the protagonist has been undermined, he hasn't merged with his demon spirit, its been too long since they came to existence, and neither he is succeeding in controlling on the thunder element.
And too much secrets, everyone keeps secret from him, as if he is some danger, he shouldn't know all that, but eventually they spill the truth, then what is the point in hiding for so long.
One more there is hero but we haven't seen his female counterpart yet, will there be any romance, i mean fantasy and all, romance is must in fantasy stories.
Just saying.....