It's not too old series, because I remember reading it a year or two ago. I remember that the story was about an Onmyouji who sealed his daughter (that he had with a demon fox) away, then a couple hundred years later, one of his descendants frees his daughter, and he (the Onmyouji) starts living in his descendant's body.
It's definitely shounen, or at least shounen-esque, but I can't remember the name, and I wanted to start reading it again and see if there had been any updates from when I stopped keeping track.
