So Shido and Rito are basically the same character in this story, so make either a oc, or a legitimate fusion of the two characters, keep kotori and Mikan as the sisters, the story of both series take place at the same time, so a much larger harem is formed, Lala can make a device to help the spirits control their powers, or even activate or turn them off, like a watch that you put a certain code in to turn them on.