Oniwakamaru the Visitor

Oniwakamaru the Visitor (異形人おに若丸) is a manga series by Tetsuya Saruwatari. It was serialized in Business Jump.

Plot
28 years earlier, there was a plane crash in the mountains of Gifu Prefecture. The barrier that the Kobo Daishi, Kukai had created to seal away the demons was destroyed in crimson flames... Present day, Oniwakamaru, King of the Yokai, appears inside the body of pure and innocent Tachibana Hitori!!