Monami makes a miraculous recovery—albeit, with one small twist—her personality and memories are that of her mother Naoko's, rather than her own. Both Heisuke and Naoko conclude that her spirit is possessing Monami's body.
This narrative suggests a supernatural element, with Monami's identity being replaced by that of her mother.  Heisuke and Naoko are convinced that this is due to a spiritual connection or possession.